With the recent bans, Pioneer is drastically changing. It turns out when you take away four cards at once, a lot of decks are impacted. As a refresher, here are the cards that just got banned in Pioneer: 

Was This the Right Move? 

Many people were prepared for Standard and Historic bans, and maybe one or two cards in Pioneer. I don't think we were ready for four cards at once.

It's a bit surprising to me. I'm not sure if I like taking all these cards out at one time, because even taking away just Inverter of Truth would have been enough to cause a shift. With that being said, if the goal was to really shake things up in a big way, these moves accomplish that. Let's break down each card individually.

The Inverter decks were too strong in Pioneer. Inverter of Truth plus Thassa's Oracle is a two-card combo that many players overlooked at first, but once it was discovered, the strategy took off in a big way. Something needed to be taken away from this deck, the question is what the best card to ban actually was. Banning Inverter means the deck is completely gone, and one of the coolest combos we have ever seen is no longer viable. After all, milling your own deck to win is unintuitive. 

There was a very real danger however that if Inverter wasn't the card banned, the deck would still remain in the format, and be too good. The other card that could have been banned instead is Dig Through Time. Dig Through Time isn't specific to Inverter decks, but undoubtedly was extremely important as a way to find the combo and fix the graveyard for when Inverter gets cast. Dig Through Time was an extremely important piece to the deck, but banning it would have hurt other decks that play it. 

In the end I'm just happy something got banned from the deck, even if Dig Through Time might have been the better choice. This is going to open up the Pioneer format in a big way, as when the format was first created the goal was for no one strategy to be too oppressive, and that seemed to be the case with the Inverter deck.

This one was surprising to me. Was Kethis a deck in Pioneer?

Magic: The Gathering TCG Deck - Kethis by genmatsu

'Kethis' - constructed deck list and prices for the Magic: The Gathering Trading Card Game from TCGplayer Infinite!

Created By: genmatsu

Event: MTGO Pioneer Challenge - 07/25/2020

Rank: 1st

Pioneer

Market Price: $590.07

Cards

Ashiok, Dream Render

Color Identity:B,U

Market Price: $1.67

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/188627_200w.jpg

Spells and abilities your opponents control can't cause their controller to search their library.
−1: Target player mills four cards. Then exile each opponent's graveyard.

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Vraska, Golgari Queen

Color Identity:B,G

Market Price: $2.78

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/176436_200w.jpg

+2: You may sacrifice another permanent. If you do, you gain 1 life and draw a card.
−3: Destroy target nonland permanent with converted mana cost 3 or less.
−9: You get an emblem with "Whenever a creature you control deals combat damage to a player, that player loses the game."

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Lavinia, Azorius Renegade

Color Identity:U,W

Market Price: $0.53

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/182131_200w.jpg

Each opponent can't cast noncreature spells with converted mana cost greater than the number of lands that player controls.
Whenever an opponent casts a spell, if no mana was spent to cast it, counter that spell.

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Garruk, Cursed Huntsman

Color Identity:B,G

Market Price: $3.35

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/198500_200w.jpg

0: Create two 2/2 black and green Wolf creature tokens with "When this creature dies, put a loyalty counter on each Garruk you control."
−3: Destroy target creature. Draw a card.
−6: You get an emblem with "Creatures you control get +3/+3 and have trample."

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Temple Garden

Color Identity:G,W

Market Price: $11.98

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/175203_200w.jpg

({T}: Add {G} or {W}.)
As Temple Garden enters the battlefield, you may pay 2 life. If you don't, it enters the battlefield tapped.

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Soul-Guide Lantern

Market Price: $0.93

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/206867_200w.jpg

When Soul-Guide Lantern enters the battlefield, exile target card from a graveyard.
{T}, Sacrifice Soul-Guide Lantern: Exile each opponent's graveyard.
{1}, {T}, Sacrifice Soul-Guide Lantern: Draw a card.

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Abrupt Decay

Color Identity:B,G

Market Price: $5.89

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/128562_200w.jpg

This spell can't be countered.
Destroy target nonland permanent with converted mana cost 3 or less.

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Emry, Lurker of the Loch

Color Identity:U

Market Price: $2.08

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/198857_200w.jpg

This spell costs {1} less to cast for each artifact you control.
When Emry, Lurker of the Loch enters the battlefield, mill four cards.
{T}: Choose target artifact card in your graveyard. You may cast that card this turn. (You still pay its costs. Timing rules still apply.)

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Hope of Ghirapur

Market Price: $2.46

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/126430_200w.jpg

Flying
Sacrifice Hope of Ghirapur: Until your next turn, target player who was dealt combat damage by Hope of Ghirapur this turn can't cast noncreature spells.

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Teferi, Time Raveler

Color Identity:U,W

Market Price: $12.88

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/187194_200w.jpg

Each opponent can cast spells only any time they could cast a sorcery.
+1: Until your next turn, you may cast sorcery spells as though they had flash.
−3: Return up to one target artifact, creature, or enchantment to its owner's hand. Draw a card.

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Jace, Wielder of Mysteries

Color Identity:U

Market Price: $7.53

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/187141_200w.jpg

If you would draw a card while your library has no cards in it, you win the game instead.
+1: Target player mills two cards. Draw a card.
−8: Draw seven cards. Then if your library has no cards in it, you win the game.

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Kethis, the Hidden Hand

Color Identity:B,G,W

Market Price: $3.05

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/192696_200w.jpg

Legendary spells you cast cost {1} less to cast.
Exile two legendary cards from your graveyard: Until end of turn, each legendary card in your graveyard gains "You may play this card from your graveyard."

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Mana Confluence

Market Price: $25.29

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/82224_200w.jpg

{T}, Pay 1 life: Add one mana of any color.

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Blooming Marsh

Color Identity:B,G

Market Price: $5.49

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/122642_200w.jpg

Blooming Marsh enters the battlefield tapped unless you control two or fewer other lands.
{T}: Add {B} or {G}.

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Lazav, the Multifarious

Color Identity:B,U

Market Price: $1.89

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/176575_200w.jpg

When Lazav, the Multifarious enters the battlefield, surveil 1. (Look at the top card of your library. You may put it into your graveyard.)
{X}: Lazav, the Multifarious becomes a copy of target creature card in your graveyard with converted mana cost X, except its name is Lazav, the Multifarious, it's legendary in addition to its other types, and it has this ability.

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Diligent Excavator

Color Identity:U

Market Price: $0.10

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/164693_200w.jpg

Whenever you cast a historic spell, target player mills two cards. (Artifacts, legendaries, and Sagas are historic.)

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Thoughtseize

Color Identity:B

Market Price: $17.11

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/218934_200w.jpg

Target player reveals their hand. You choose a nonland card from it. That player discards that card. You lose 2 life.

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Urborg, Tomb of Yawgmoth

Market Price: $15.06

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/234275_200w.jpg

Each land is a Swamp in addition to its other land types.

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Hallowed Fountain

Color Identity:U,W

Market Price: $8.68

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/182831_200w.jpg

({T}: Add {W} or {U}.)
As Hallowed Fountain enters the battlefield, you may pay 2 life. If you don't, it enters the battlefield tapped.

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Teshar, Ancestor's Apostle

Color Identity:W

Market Price: $0.44

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/162209_200w.jpg

Flying
Whenever you cast a historic spell, return target creature card with converted mana cost 3 or less from your graveyard to the battlefield. (Artifacts, legendaries, and Sagas are historic.)

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Urza's Ruinous Blast

Color Identity:W

Market Price: $2.17

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/162211_200w.jpg

(You may cast a legendary sorcery only if you control a legendary creature or planeswalker.)
Exile all nonland permanents that aren't legendary.

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Mox Amber

Market Price: $33.80

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/162125_200w.jpg

{T}: Add one mana of any color among legendary creatures and planeswalkers you control.

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Liliana, the Last Hope

Color Identity:B

Market Price: $25.86

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/120266_200w.jpg

+1: Up to one target creature gets -2/-1 until your next turn.
−2: Mill two cards, then you may return a creature card from your graveyard to your hand.
−7: You get an emblem with "At the beginning of your end step, create X 2/2 black Zombie creature tokens, where X is two plus the number of Zombies you control."

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Kambal, Consul of Allocation

Color Identity:B,W

Market Price: $4.80

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/122729_200w.jpg

Whenever an opponent casts a noncreature spell, that player loses 2 life and you gain 2 life.

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Breeding Pool

Color Identity:G,U

Market Price: $23.55

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/182842_200w.jpg

({T}: Add {G} or {U}.)
As Breeding Pool enters the battlefield, you may pay 2 life. If you don't, it enters the battlefield tapped.

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Lurrus of the Dream-Den

Color Identity:B,W

Market Price: $11.75

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/212282_200w.jpg

Companion — Each permanent card in your starting deck has converted mana cost 2 or less. (If this card is your chosen companion, you may put it into your hand from outside the game for {3} any time you could cast a sorcery.)
Lifelink
During each of your turns, you may cast one permanent spell with converted mana cost 2 or less from your graveyard.

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Ashiok, Nightmare Muse

Color Identity:B,U

Market Price: $3.78

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/206007_200w.jpg

+1: Create a 2/3 blue and black Nightmare creature token with "Whenever this creature attacks or blocks, each opponent exiles the top two cards of their library."
−3: Return target nonland permanent to its owner's hand, then that player exiles a card from their hand.
−7: You may cast up to three spells from among face-up cards your opponents own from exile without paying their mana costs.

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Fatal Push

Color Identity:B

Market Price: $2.00

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/218830_200w.jpg

Destroy target creature if it has converted mana cost 2 or less.
Revolt — Destroy that creature if it has converted mana cost 4 or less instead if a permanent you controlled left the battlefield this turn.

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Tamiyo, Collector of Tales

Color Identity:G,U

Market Price: $0.92

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/188490_200w.jpg

Spells and abilities your opponents control can't cause you to discard cards or sacrifice permanents.
+1: Choose a nonland card name, then reveal the top four cards of your library. Put all cards with the chosen name from among them into your hand and the rest into your graveyard.
−3: Return target card from your graveyard to your hand.

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Oath of Nissa

Color Identity:G

Market Price: $2.87

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/110818_200w.jpg

When Oath of Nissa enters the battlefield, look at the top three cards of your library. You may reveal a creature, land, or planeswalker card from among them and put it into your hand. Put the rest on the bottom of your library in any order.
You may spend mana as though it were mana of any color to cast planeswalker spells.

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Botanical Sanctum

Color Identity:G,U

Market Price: $4.44

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/122643_200w.jpg

Botanical Sanctum enters the battlefield tapped unless you control two or fewer other lands.
{T}: Add {G} or {U}.

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Uro, Titan of Nature's Wrath

Color Identity:G,U

Market Price: $18.88

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/206836_200w.jpg

When Uro enters the battlefield, sacrifice it unless it escaped.
Whenever Uro enters the battlefield or attacks, you gain 3 life and draw a card, then you may put a land card from your hand onto the battlefield.
Escape—{G}{G}{U}{U}, Exile five other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)

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Yes. However, it was still less than 5 percent of the metagame. I don't think Kethis, the Hidden Hand really got its time to shine in Pioneer before it got banned. It likely would have started to see a lot more play though after these bans, and maybe would have become the best deck. When I think back to the last paper MTG event I participated in, Players Tour Phoenix, where Pioneer was played, Kethis basically wasn't a deck. 

Recently the deck had been gaining some momentum, but still looks very similar to the version we have seen in Historic. Reading over the reasons why Wizards of the Coast decided to ban Kethis, the Hidden Hand, it appears they want to significantly reduce the power level of combo decks in general. While I understand wanting to hurt combo, I don't think this is a valid reason for banning Kethis. Every other card banned is also a combo card, and you don't need to make a 360 degree turn in the format with one ban announcement. However, they do point to Kethis Combo going 5-0 in MTGO quite a lot. This is the best argument for banning Kethis in my opinion, but I think it was a little too soon. 

I mentioned that every card on this list is a combo card, and while that's true, Walking Ballista falls in a bit of a grey area. It provides a one-two punch alongside Heliod, Sun-Crowned, but it is also just a high-quality creature that can be played in a variety of strategies. The goal in banning Walking Ballista was to target the Heliod decks, but there are other strategies that will get hurt as well. Think about the Golgari counters deck with Winding Constrictor for example. That was a deck we saw players playing at the start of the Pioneer format, and Walking Ballista was definitely an important creature to have access to. 

An alternative to banning Walking Ballista would have been banning Heliod, Sun-Crowned instead. It's understandable to not want a two card-combo that straight up wins the game in the format. In fact, I do think the combo was too good, but I probably would have banned Heliod. Mono-White Devotion has been hit so hard by this, I don't expect it to bounce back without one of its key cards. 

Now we get to Underworld Breach, perhaps the most interesting ban of all four.

Magic: The Gathering TCG Deck - Lotus Breach by _INF_

'Lotus Breach' - constructed deck list and prices for the Magic: The Gathering Trading Card Game from TCGplayer Infinite!

Created By: _INF_

Event: MTGO Pioneer Challenge - 07/25/2020

Rank: 3rd-4th

Pioneer

Market Price: $199.01

Cards

Thespian's Stage

Market Price: $1.56

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/218436_200w.jpg

{T}: Add {C}.
{2}, {T}: Thespian's Stage becomes a copy of target land, except it has this ability.

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Fae of Wishes // Granted

Color Identity:U

Market Price: $0.25

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/199346_200w.jpg

Buy This Card! https://shop.tcgplayer.com/magic/throne-of-eldraine/fae-of-wishes

Arboreal Grazer

Color Identity:G

Market Price: $0.28

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/188872_200w.jpg

Reach
When Arboreal Grazer enters the battlefield, you may put a land card from your hand onto the battlefield tapped.

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Supreme Verdict

Color Identity:U,W

Market Price: $6.56

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/145308_200w.jpg

This spell can't be countered.
Destroy all creatures.

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Temple of Mystery

Color Identity:G,U

Market Price: $1.00

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/236345_200w.jpg

Temple of Mystery enters the battlefield tapped.
When Temple of Mystery enters the battlefield, scry 1.
{T}: Add {G} or {U}.

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Sylvan Scrying

Color Identity:G

Market Price: $0.93

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/105272_200w.jpg

Search your library for a land card, reveal it, and put it into your hand. Then shuffle your library.

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Ipnu Rivulet

Color Identity:U

Market Price: $0.10

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/135090_200w.jpg

{T}: Add {C}.
{T}, Pay 1 life: Add {U}.
{1}{U}, {T}, Sacrifice a Desert: Target player mills four cards.

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Blast Zone

Market Price: $4.25

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/188636_200w.jpg

Blast Zone enters the battlefield with a charge counter on it.
{T}: Add {C}.
{X}{X}, {T}: Put X charge counters on Blast Zone.
{3}, {T}, Sacrifice Blast Zone: Destroy each nonland permanent with converted mana cost equal to the number of charge counters on Blast Zone.

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Wilt

Color Identity:G

Market Price: $0.20

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/212274_200w.jpg

Destroy target artifact or enchantment.
Cycling {2} ({2}, Discard this card: Draw a card.)

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See the Truth

Color Identity:U

Market Price: $0.38

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/215540_200w.jpg

Look at the top three cards of your library. Put one of those cards into your hand and the rest on the bottom of your library in any order. If this spell was cast from anywhere other than your hand, put each of those cards into your hand instead.

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Strategic Planning

Color Identity:U

Market Price: $0.01

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230725_200w.jpg

Look at the top three cards of your library. Put one of them into your hand and the rest into your graveyard.

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Vizier of Tumbling Sands

Color Identity:U

Market Price: $0.10

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/212370_200w.jpg

{T}: Untap another target permanent.
Cycling {1}{U} ({1}{U}, Discard this card: Draw a card.)
When you cycle Vizier of Tumbling Sands, untap target permanent.

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Underworld Breach

Color Identity:R

Market Price: $8.31

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/206642_200w.jpg

Each nonland card in your graveyard has escape. The escape cost is equal to the card's mana cost plus exile three other cards from your graveyard. (You may cast cards from your graveyard for their escape cost.)
At the beginning of the end step, sacrifice Underworld Breach.

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Jace, Wielder of Mysteries

Color Identity:U

Market Price: $7.53

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/187141_200w.jpg

If you would draw a card while your library has no cards in it, you win the game instead.
+1: Target player mills two cards. Draw a card.
−8: Draw seven cards. Then if your library has no cards in it, you win the game.

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Ugin, the Spirit Dragon

Market Price: $31.63

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/215338_200w.jpg

+2: Ugin, the Spirit Dragon deals 3 damage to any target.
−X: Exile each permanent with converted mana cost X or less that's one or more colors.
−10: You gain 7 life, draw seven cards, then put up to seven permanent cards from your hand onto the battlefield.

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Thassa's Oracle

Color Identity:U

Market Price: $15.07

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/206926_200w.jpg

When Thassa's Oracle enters the battlefield, look at the top X cards of your library, where X is your devotion to blue. Put up to one of them on top of your library and the rest on the bottom of your library in a random order. If X is greater than or equal to the number of cards in your library, you win the game. (Each {U} in the mana costs of permanents you control counts toward your devotion to blue.)

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Nine Lives

Color Identity:W

Market Price: $0.32

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/215700_200w.jpg

Hexproof
If a source would deal damage to you, prevent that damage and put an incarnation counter on Nine Lives.
When there are nine or more incarnation counters on Nine Lives, exile it.
When Nine Lives leaves the battlefield, you lose the game.

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Thought Distortion

Color Identity:B

Market Price: $0.09

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/192531_200w.jpg

This spell can't be countered.
Target opponent reveals their hand. Exile all noncreature, nonland cards from that player's hand and graveyard.

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Hidden Strings

Color Identity:U

Market Price: $0.25

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/67963_200w.jpg

You may tap or untap target permanent, then you may tap or untap another target permanent.
Cipher (Then you may exile this spell card encoded on a creature you control. Whenever that creature deals combat damage to a player, its controller may cast a copy of the encoded card without paying its mana cost.)

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Botanical Sanctum

Color Identity:G,U

Market Price: $4.44

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/122643_200w.jpg

Botanical Sanctum enters the battlefield tapped unless you control two or fewer other lands.
{T}: Add {G} or {U}.

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Mystical Dispute

Color Identity:U

Market Price: $0.32

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/198683_200w.jpg

This spell costs {2} less to cast if it targets a blue spell.
Counter target spell unless its controller pays {3}.

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Sheltered Thicket

Color Identity:G,R

Market Price: $2.70

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/129685_200w.jpg

({T}: Add {R} or {G}.)
Sheltered Thicket enters the battlefield tapped.
Cycling {2} ({2}, Discard this card: Draw a card.)

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Island

Color Identity:U

Market Price: $0.43

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/235542_200w.jpg

({T}: Add {U}.)

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Blink of an Eye

Color Identity:U

Market Price: $0.23

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/162214_200w.jpg

Kicker {1}{U} (You may pay an additional {1}{U} as you cast this spell.)
Return target nonland permanent to its owner's hand. If this spell was kicked, draw a card.

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Discontinuity

Color Identity:U

Market Price: $1.53

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/215672_200w.jpg

As long as it's your turn, this spell costs {2}{U}{U} less to cast.
End the turn. (Exile all spells and abilities from the stack, including this card. The player whose turn it is discards down to their maximum hand size. Damage wears off, and "this turn" and "until end of turn" effects end.)

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Anger of the Gods

Color Identity:R

Market Price: $1.07

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/145342_200w.jpg

Anger of the Gods deals 3 damage to each creature. If a creature dealt damage this way would die this turn, exile it instead.

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Breeding Pool

Color Identity:G,U

Market Price: $23.55

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/182842_200w.jpg

({T}: Add {G} or {U}.)
As Breeding Pool enters the battlefield, you may pay 2 life. If you don't, it enters the battlefield tapped.

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Pore Over the Pages

Color Identity:U

Market Price: $0.16

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/114870_200w.jpg

Draw three cards, untap up to two lands, then discard a card.

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Yavimaya Coast

Color Identity:G,U

Market Price: $1.00

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/236347_200w.jpg

{T}: Add {C}.
{T}: Add {G} or {U}. Yavimaya Coast deals 1 damage to you.

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Tome Scour

Color Identity:U

Market Price: $0.22

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/69967_200w.jpg

Target player mills five cards.

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Lotus Field

Market Price: $8.95

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/192640_200w.jpg

Hexproof
Lotus Field enters the battlefield tapped.
When Lotus Field enters the battlefield, sacrifice two lands.
{T}: Add three mana of any one color.

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Lotus Breach is a deck that had grown in popularity—in fact it's the deck I personally have played the most in Pioneer. This is another really sweet combo strategy, unlike any deck we have ever seen before. Underworld Breach saw a little bit of play outside of Lotus Breach, but primarily Lotus Breach was the main home for this card. 

The funny thing is that Underworld Breach wasn't the only reason why the Lotus Field deck is good. The combo of Lotus Field plus Thespian's Stage to have two Lotus Fields (and then use untap effects to generate a ton of mana) existed before Underworld Breach was Pioneer-legal. Taking away Breach will hurt the strategy, but won't come close to killing it off. In the case of all the other combo decks I have talked about so far, the combo decks more or less are no longer viable now, yet here WotC went in a different direction. 

We have already been seeing players start to build new Lotus decks, and find success, even in these few days since the ban announcement. Ben Breslow posted his recent 5-0 in a Pioneer Prelim with this list:

Magic: The Gathering TCG Deck - Lotus Field by Ben Breslow

'Lotus Field' - constructed deck list and prices for the Magic: The Gathering Trading Card Game from TCGplayer Infinite!

Created By: Ben Breslow

Event:

Rank:

Pioneer

Market Price: $104.62

Cards

Hidden Strings

Color Identity:U

Market Price: $0.25

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/67963_200w.jpg

You may tap or untap target permanent, then you may tap or untap another target permanent.
Cipher (Then you may exile this spell card encoded on a creature you control. Whenever that creature deals combat damage to a player, its controller may cast a copy of the encoded card without paying its mana cost.)

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Botanical Sanctum

Color Identity:G,U

Market Price: $4.44

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/122643_200w.jpg

Botanical Sanctum enters the battlefield tapped unless you control two or fewer other lands.
{T}: Add {G} or {U}.

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Mystical Dispute

Color Identity:U

Market Price: $0.32

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/198683_200w.jpg

This spell costs {2} less to cast if it targets a blue spell.
Counter target spell unless its controller pays {3}.

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Yavimaya Coast

Color Identity:G,U

Market Price: $1.00

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/236347_200w.jpg

{T}: Add {C}.
{T}: Add {G} or {U}. Yavimaya Coast deals 1 damage to you.

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Shifting Ceratops

Color Identity:G

Market Price: $0.19

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/192635_200w.jpg

This spell can't be countered.
Protection from blue (This creature can't be blocked, targeted, dealt damage, enchanted, or equipped by anything blue.)
{G}: Shifting Ceratops gains your choice of reach, trample, or haste until end of turn.

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Dig Through Time

Color Identity:U

Market Price: $1.49

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/236207_200w.jpg

Delve (Each card you exile from your graveyard while casting this spell pays for {1}.)
Look at the top seven cards of your library. Put two of them into your hand and the rest on the bottom of your library in any order.

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Expansion // Explosion

Color Identity:R,U

Market Price: $2.45

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/176440_200w.jpg

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Wilt

Color Identity:G

Market Price: $0.20

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/212274_200w.jpg

Destroy target artifact or enchantment.
Cycling {2} ({2}, Discard this card: Draw a card.)

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Temple of Mystery

Color Identity:G,U

Market Price: $1.00

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/236345_200w.jpg

Temple of Mystery enters the battlefield tapped.
When Temple of Mystery enters the battlefield, scry 1.
{T}: Add {G} or {U}.

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Lotus Field

Market Price: $8.95

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/192640_200w.jpg

Hexproof
Lotus Field enters the battlefield tapped.
When Lotus Field enters the battlefield, sacrifice two lands.
{T}: Add three mana of any one color.

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Anger of the Gods

Color Identity:R

Market Price: $1.07

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/145342_200w.jpg

Anger of the Gods deals 3 damage to each creature. If a creature dealt damage this way would die this turn, exile it instead.

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Ral, Storm Conduit

Color Identity:R,U

Market Price: $2.00

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/188346_200w.jpg

Whenever you cast or copy an instant or sorcery spell, Ral, Storm Conduit deals 1 damage to target opponent or planeswalker.
+2: Scry 1.
−2: When you cast your next instant or sorcery spell this turn, copy that spell. You may choose new targets for the copy.

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Niv-Mizzet, Parun

Color Identity:R,U

Market Price: $3.25

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/175582_200w.jpg

This spell can't be countered.
Flying
Whenever you draw a card, Niv-Mizzet, Parun deals 1 damage to any target.
Whenever a player casts an instant or sorcery spell, you draw a card.

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Doublecast

Color Identity:R

Market Price: $0.37

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/216615_200w.jpg

When you cast your next instant or sorcery spell this turn, copy that spell. You may choose new targets for the copy.

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Blast Zone

Market Price: $4.25

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/188636_200w.jpg

Blast Zone enters the battlefield with a charge counter on it.
{T}: Add {C}.
{X}{X}, {T}: Put X charge counters on Blast Zone.
{3}, {T}, Sacrifice Blast Zone: Destroy each nonland permanent with converted mana cost equal to the number of charge counters on Blast Zone.

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Arboreal Grazer

Color Identity:G

Market Price: $0.28

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/188872_200w.jpg

Reach
When Arboreal Grazer enters the battlefield, you may put a land card from your hand onto the battlefield tapped.

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Opt

Color Identity:U

Market Price: $0.13

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/215840_200w.jpg

Scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)
Draw a card.

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Sylvan Scrying

Color Identity:G

Market Price: $0.93

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/105272_200w.jpg

Search your library for a land card, reveal it, and put it into your hand. Then shuffle your library.

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Thespian's Stage

Market Price: $1.56

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/218436_200w.jpg

{T}: Add {C}.
{2}, {T}: Thespian's Stage becomes a copy of target land, except it has this ability.

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Vizier of Tumbling Sands

Color Identity:U

Market Price: $0.10

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/212370_200w.jpg

{T}: Untap another target permanent.
Cycling {1}{U} ({1}{U}, Discard this card: Draw a card.)
When you cycle Vizier of Tumbling Sands, untap target permanent.

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Island

Color Identity:U

Market Price: $0.43

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/235542_200w.jpg

({T}: Add {U}.)

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Pore Over the Pages

Color Identity:U

Market Price: $0.16

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/114870_200w.jpg

Draw three cards, untap up to two lands, then discard a card.

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Aether Gust

Color Identity:U

Market Price: $0.74

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/192535_200w.jpg

Choose target spell or permanent that's red or green. Its owner puts it on the top or bottom of their library.

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Strategic Planning

Color Identity:U

Market Price: $0.01

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230725_200w.jpg

Look at the top three cards of your library. Put one of them into your hand and the rest into your graveyard.

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This is a really impressive and innovative list, especially given how soon it was built after the recent bans. The game plan revolves around copying your instants and sorceries with cards like Doublecast and Ral, Storm Conduit. While Expansion // Explosion can copy spells as well, the card is also the primary win condition. There aren't any Fae of Wishes here, though you could build a different variant of the strategy that does win with Fae instead. 

We see here where Dig Through Time can be fully utilized. Casting two Dig Through Time at once (by copying one) is almost always going to allow you to find the combo pieces that you are looking for. The bonus of not playing Fae of Wishes in the deck is you actually get to play a full sideboard, rather than a bunch of one-ofs. I expect to see plenty of versions of this deck moving forward, as the race to find the optimal list without Underworld Breach has already started. 

What Happens to Pioneer with Less Combo? 

This is the big question. It's clear that there won't be as many combo decks in the format, which means there is a very real chance Pioneer will start to look similar to Historic. The combo decks that do exist are now easier to target, because you can devote more sideboard cards to them.

In the world where the Lotus Field deck is the only good combo deck in the format, it's not going to be difficult to target it by putting some Damping Sphere in your sideboard. Having less combo in the format indirectly hurts the combo decks that do still exist, because they are easier to target when constructing a full 75. This leads to the aggro vs midrange vs control battle. 

The decks that tend to come out on top here are midrange strategies, and possibly even a deck like Azorius Control. Aggro decks are easier to target when a format shrinks, in a similar way that is the case with combo. Putting more removal or life gain in your deck is a clear way to build a deck that will be better against aggro. Sultai Delirium is a classic midrange option, and Niv to Light works as a midrange deck with a combo built in. 

In general, when so many cards are banned, decks that already existed and didn't have cards taken away from them will stand to benefit. Certainly Mono-Black Aggro isn't going anywhere. The same can be said for Spirits, Mono-Green Stompy, Mono-Red variants and Izzet Ensoul. I actually wouldn't be surprised if we start to see Wilderness Reclamation decks pop up more, now that Pioneer will be the main home for that card moving forward.