I'm not gonna bury the lede here:

This is one of the more powerful and flexible spells we've seen in some time. Normally, weird narrow combo cards have the downside of being dead outside of the combo itself. Mystic Reflection is part combo piece, part counterspell, and altogether incredibly cheap. Provided you are playing with (or against) creatures, Mystic Reflection can be used to turn powerful threats into the weakest creature on the battlefield. Your opponent is casting Ugin, the Spirit Dragon? Cast Mystic Reflection targeting your Heart's Desire token. 

Now this power does have some restrictions. You cannot target legendary creatures. The targeted creature must still be around when Mystic Reflection resolves. The effect only occurs for the next instance and not the entire turn. 

As "countermagic," Mystic Reflection is at its best against expensive threats that take up most of your opponent's mana. As a combo piece, Mystic Reflection wants to burst token generation that doesn't rely on individual triggers:

The more bodies you can put in play at the same time, the better! Reverent Hoplite is a special case where it can be both the target of and the enabler for Mystic Reflection. All of these cards have fairly strict requirements, though, as there's not an efficient x spell to make tokens with in Standard.  

What exactly are we turning all these tokens into? Large bodies, incredible ETB effects, and non-legendary lords. There are far too many enticing "clone" targets in Standard to count, but how about some example decklists?

Magic: The Gathering TCG Deck - Azorius Yorion Reflection by Yoman5

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

Created By: Yoman5

Event:

Rank:

Standard

Market Price: $168.22

Cards

Skyclave Apparition

Color Identity:W

Market Price: $8.65

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/221860_200w.jpg

When Skyclave Apparition enters the battlefield, exile up to one target nonland, nontoken permanent you don't control with converted mana cost 4 or less.
When Skyclave Apparition leaves the battlefield, the exiled card's owner creates an X/X blue Illusion creature token, where X is the converted mana cost of the exiled card.

Buy This Card! https://shop.tcgplayer.com/magic/zendikar-rising/skyclave-apparition

Temple of Enlightenment

Color Identity:U,W

Market Price: $0.78

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/206634_200w.jpg

Temple of Enlightenment enters the battlefield tapped.
When Temple of Enlightenment enters the battlefield, scry 1. (Look at the top card of your library. You may put that card on the bottom of your library.)
{T}: Add {W} or {U}.

Buy This Card! https://shop.tcgplayer.com/magic/theros-beyond-death/temple-of-enlightenment

Snow-Covered Plains

Color Identity:W

Market Price: $0.23

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230147_200w.jpg

({T}: Add {W}.)

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/snow-covered-plains-276

Shatter the Sky

Color Identity:W

Market Price: $0.78

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/207069_200w.jpg

Each player who controls a creature with power 4 or greater draws a card. Then destroy all creatures.

Buy This Card! https://shop.tcgplayer.com/magic/theros-beyond-death/shatter-the-sky

Elspeth Conquers Death

Color Identity:W

Market Price: $1.65

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/207052_200w.jpg

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Exile target permanent an opponent controls with converted mana cost 3 or greater.
II — Noncreature spells your opponents cast cost {2} more to cast until your next turn.
III — Return target creature or planeswalker card from your graveyard to the battlefield. Put a +1/+1 counter or a loyalty counter on it.

Buy This Card! https://shop.tcgplayer.com/magic/theros-beyond-death/elspeth-conquers-death

Yorion, Sky Nomad

Color Identity:U,W

Market Price: $2.70

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/212715_200w.jpg

Companion — Your starting deck contains at least twenty cards more than the minimum deck size. (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.)
Flying
When Yorion enters the battlefield, exile any number of other nonland permanents you own and control. Return those cards to the battlefield at the beginning of the next end step.

Buy This Card! https://shop.tcgplayer.com/magic/ikoria-lair-of-behemoths/yorion-sky-nomad

Mazemind Tome

Market Price: $2.51

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/215519_200w.jpg

{T}, Put a page counter on Mazemind Tome: Scry 1.
{2}, {T}, Put a page counter on Mazemind Tome: Draw a card.
When there are four or more page counters on Mazemind Tome, exile it. If you do, you gain 4 life.

Buy This Card! https://shop.tcgplayer.com/magic/core-set-2021/mazemind-tome

The Birth of Meletis

Color Identity:W

Market Price: $0.44

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/206752_200w.jpg

(As this Saga enters and after your draw step, add a lore counter. Sacrifice after III.)
I — Search your library for a basic Plains card, reveal it, put it into your hand, then shuffle your library.
II — Create a 0/4 colorless Wall artifact creature token with defender.
III — You gain 2 life.

Buy This Card! https://shop.tcgplayer.com/magic/theros-beyond-death/the-birth-of-meletis

Dream Trawler

Color Identity:U,W

Market Price: $0.67

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/207050_200w.jpg

Flying, lifelink
Whenever you draw a card, Dream Trawler gets +1/+0 until end of turn.
Whenever Dream Trawler attacks, draw a card.
Discard a card: Dream Trawler gains hexproof until end of turn. Tap it.

Buy This Card! https://shop.tcgplayer.com/magic/theros-beyond-death/dream-trawler

Omen of the Sun

Color Identity:W

Market Price: $0.09

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/206784_200w.jpg

Flash
When Omen of the Sun enters the battlefield, create two 1/1 white Human Soldier creature tokens and you gain 2 life.
{2}{W}, Sacrifice Omen of the Sun: Scry 2.

Buy This Card! https://shop.tcgplayer.com/magic/theros-beyond-death/omen-of-the-sun

Emeria's Call // Emeria, Shattered Skyclave

Color Identity:W

Market Price: $3.34

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/221952_200w.jpg

Create two 4/4 white Angel Warrior creature tokens with flying. Non-Angel creatures you control gain indestructible until your next turn.

Buy This Card! https://shop.tcgplayer.com/magic/zendikar-rising/emerias-call

Hengegate Pathway // Mistgate Pathway

Color Identity:U,W

Market Price: $3.66

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/229207_200w.jpg

{T}: Add {W}.

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/hengegate-pathway

Castle Vantress

Color Identity:U

Market Price: $0.76

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/199284_200w.jpg

Castle Vantress enters the battlefield tapped unless you control an Island.
{T}: Add {U}.
{2}{U}{U}, {T}: Scry 2.

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

Solemn Simulacrum

Market Price: $1.39

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/215510_200w.jpg

When Solemn Simulacrum enters the battlefield, you may search your library for a basic land card, put that card onto the battlefield tapped, then shuffle your library.
When Solemn Simulacrum dies, you may draw a card.

Buy This Card! https://shop.tcgplayer.com/magic/core-set-2021/solemn-simulacrum

Fabled Passage

Market Price: $7.89

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/215556_200w.jpg

{T}, Sacrifice Fabled Passage: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle your library. Then if you control four or more lands, untap that land.

Buy This Card! https://shop.tcgplayer.com/magic/core-set-2021/fabled-passage

Omen of the Sea

Color Identity:U

Market Price: $0.09

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/206769_200w.jpg

Flash
When Omen of the Sea enters the battlefield, scry 2, then draw a card.
{2}{U}, Sacrifice Omen of the Sea: Scry 2.

Buy This Card! https://shop.tcgplayer.com/magic/theros-beyond-death/omen-of-the-sea

Jwari Disruption // Jwari Ruins

Color Identity:U

Market Price: $0.25

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/222101_200w.jpg

Counter target spell unless its controller pays {1}.

Buy This Card! https://shop.tcgplayer.com/magic/zendikar-rising/jwari-disruption

Mystic Reflection

Color Identity:U

Market Price: $5.18

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230497_200w.jpg

Choose target nonlegendary creature. The next time one or more creatures or planeswalkers enter the battlefield this turn, they enter as copies of the chosen creature.
Foretell {U} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/mystic-reflection

Glass Casket

Color Identity:W

Market Price: $0.18

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/199004_200w.jpg

When Glass Casket enters the battlefield, exile target creature an opponent controls with converted mana cost 3 or less until Glass Casket leaves the battlefield.

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

Snow-Covered Island

Color Identity:U

Market Price: $0.97

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230148_200w.jpg

({T}: Add {U}.)

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/snow-covered-island-278

Pretty tame, boring way to use the card, but turning Birth of Meletis tokens or bodies from Omen of the Sun into Solemn Simulacrum, Skyclave Apparition, or Dream Trawler is powerful. This is just adding a good card to an existing deck. Let's go a little further. 

Magic: The Gathering TCG Deck - Sultai” Elf Reflection by Yoman5

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

Created By: Yoman5

Event:

Rank:

Standard

Market Price: $125.08

Cards

Barkchannel Pathway // Tidechannel Pathway

Color Identity:G,U

Market Price: $3.35

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/229210_200w.jpg

{T}: Add {G}.

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/barkchannel-pathway

Canopy Tactician

Color Identity:G

Market Price: $0.89

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/229267_200w.jpg

Other Elves you control get +1/+1.
{T}: Add {G}{G}{G}.

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/canopy-tactician

Jaspera Sentinel

Color Identity:G

Market Price: $0.02

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230447_200w.jpg

Reach
{T}, Tap an untapped creature you control: Add one mana of any color.

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/jaspera-sentinel

Mystic Reflection

Color Identity:U

Market Price: $5.18

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230497_200w.jpg

Choose target nonlegendary creature. The next time one or more creatures or planeswalkers enter the battlefield this turn, they enter as copies of the chosen creature.
Foretell {U} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/mystic-reflection

Sculptor of Winter

Color Identity:G

Market Price: $0.02

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230156_200w.jpg

{T}: Untap target snow land.

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/sculptor-of-winter

Snow-Covered Forest

Color Identity:G

Market Price: $0.70

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230146_200w.jpg

({T}: Add {G}.)

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/snow-covered-forest-284

Zagoth Triome

Color Identity:B,G,U

Market Price: $11.27

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/212691_200w.jpg

({T}: Add {B}, {G}, or {U}.)
Zagoth Triome enters the battlefield tapped.
Cycling {3} ({3}, Discard this card: Draw a card.)

Buy This Card! https://shop.tcgplayer.com/magic/ikoria-lair-of-behemoths/zagoth-triome

Llanowar Visionary

Color Identity:G

Market Price: $0.25

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/215462_200w.jpg

When Llanowar Visionary enters the battlefield, draw a card.
{T}: Add {G}.

Buy This Card! https://shop.tcgplayer.com/magic/core-set-2021/llanowar-visionary

Darkbore Pathway // Slitherbore Pathway

Color Identity:B,G

Market Price: $5.03

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/229208_200w.jpg

{T}: Add {B}.

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/darkbore-pathway

Realmwalker

Color Identity:G

Market Price: $2.09

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/229251_200w.jpg

Changeling (This card is every creature type.)
As Realmwalker enters the battlefield, choose a creature type.
You may look at the top card of your library any time.
You may cast creature spells of the chosen type from the top of your library.

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/realmwalker

Elven Ambush

Color Identity:G

Market Price: $0.51

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/229274_200w.jpg

Create a 1/1 green Elf Warrior creature token for each Elf you control.

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/elven-ambush

Elvish Warmaster

Color Identity:G

Market Price: $1.58

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230124_200w.jpg

Whenever one or more other Elves enter the battlefield under your control, create a 1/1 green Elf Warrior creature token. This ability triggers only once each turn.
{5}{G}{G}: Elves you control get +2/+2 and gain deathtouch until end of turn.

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/elvish-warmaster

Skemfar Shadowsage

Color Identity:B

Market Price: $0.06

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230204_200w.jpg

When Skemfar Shadowsage enters the battlefield, choose one —
• Each opponent loses X life, where X is the greatest number of creatures you control that have a creature type in common.
• You gain X life, where X is the greatest number of creatures you control that have a creature type in common.

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/skemfar-shadowsage

Have you ever wanted to make a dozen elf lords at instant speed? How about a whole bunch of Skemfar Shadowsages to burn your opponent out? This is a mono-green elves deck capable of doing normal elves things and just curving out, but also had Mystic Reflection to turn one of those Elf tokens or cheap creatures into another Canopy Tactician or Skemfar Shadowsage.

Reaching beyond Standard into Historic, we get some more interesting enablers:

March of the Multitudes is capable of making a ton of bodies at instant speed while leaving up enough mana to cast Mystic Reflection, and Hornet Queen is an enabler target like Reverent Hoplite. Cauldron Familiar is where it gets interesting. Cauldron Familiar is a resilient body to always have available for the counterspell mode of Mystic Reflection, while also having access to a zero-mana body on command to copy the best creature on the battlefield. 

Magic: The Gathering TCG Deck - Grixis Sacrifice by Yoman5

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

Created By: Yoman5

Event:

Rank:

Historic

Market Price: $230.99

Cards

Watery Grave

Color Identity:B,U

Market Price: $9.53

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/175205_200w.jpg

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

Buy This Card! https://shop.tcgplayer.com/magic/guilds-of-ravnica/watery-grave

Claim the Firstborn

Color Identity:R

Market Price: $0.34

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/198858_200w.jpg

Gain control of target creature with converted mana cost 3 or less until end of turn. Untap that creature. It gains haste until end of turn.

Buy This Card! https://shop.tcgplayer.com/magic/throne-of-eldraine/claim-the-firstborn

Island

Color Identity:U

Market Price: $0.21

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230465_200w.jpg

({T}: Add {U}.)

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/island

Blightstep Pathway // Searstep Pathway

Color Identity:B,R

Market Price: $3.71

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/229209_200w.jpg

{T}: Add {B}.

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/blightstep-pathway

Steam Vents

Color Identity:R,U

Market Price: $9.67

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/175202_200w.jpg

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

Buy This Card! https://shop.tcgplayer.com/magic/guilds-of-ravnica/steam-vents

Priest of Forgotten Gods

Color Identity:B

Market Price: $3.24

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/183311_200w.jpg

{T}, Sacrifice two other creatures: Any number of target players each lose 2 life and sacrifice a creature. You add {B}{B} and draw a card.

Buy This Card! https://shop.tcgplayer.com/magic/ravnica-allegiance/priest-of-forgotten-gods

Witch's Oven

Market Price: $0.23

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/198898_200w.jpg

{T}, Sacrifice a creature: Create a Food token. If the sacrificed creature's toughness was 4 or greater, create two Food tokens instead. (They're artifacts with "{2}, {T}, Sacrifice this artifact: You gain 3 life.")

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

Blood Crypt

Color Identity:B,R

Market Price: $16.72

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/182838_200w.jpg

({T}: Add {B} or {R}.)
As Blood Crypt enters the battlefield, you may pay 2 life. If you don't, it enters the battlefield tapped.

Buy This Card! https://shop.tcgplayer.com/magic/ravnica-allegiance/blood-crypt

Midnight Reaper

Color Identity:B

Market Price: $0.44

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/176429_200w.jpg

Whenever a nontoken creature you control dies, Midnight Reaper deals 1 damage to you and you draw a card.

Buy This Card! https://shop.tcgplayer.com/magic/guilds-of-ravnica/midnight-reaper

Fabled Passage

Market Price: $7.89

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/215556_200w.jpg

{T}, Sacrifice Fabled Passage: Search your library for a basic land card, put it onto the battlefield tapped, then shuffle your library. Then if you control four or more lands, untap that land.

Buy This Card! https://shop.tcgplayer.com/magic/core-set-2021/fabled-passage

Mountain

Color Identity:R

Market Price: $0.33

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230467_200w.jpg

({T}: Add {R}.)

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/mountain

Swamp

Color Identity:B

Market Price: $0.15

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230466_200w.jpg

({T}: Add {B}.)

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/swamp

Mystic Reflection

Color Identity:U

Market Price: $5.18

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/230497_200w.jpg

Choose target nonlegendary creature. The next time one or more creatures or planeswalkers enter the battlefield this turn, they enter as copies of the chosen creature.
Foretell {U} (During your turn, you may pay {2} and exile this card from your hand face down. Cast it on a later turn for its foretell cost.)

Buy This Card! https://shop.tcgplayer.com/magic/kaldheim/mystic-reflection

Cauldron Familiar

Color Identity:B

Market Price: $0.42

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/215972_200w.jpg

When Cauldron Familiar enters the battlefield, each opponent loses 1 life and you gain 1 life.
Sacrifice a Food: Return Cauldron Familiar from your graveyard to the battlefield.

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Chandra, Torch of Defiance

Color Identity:R

Market Price: $6.03

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/122645_200w.jpg

+1: Exile the top card of your library. You may cast that card. If you don't, Chandra, Torch of Defiance deals 2 damage to each opponent.
+1: Add {R}{R}.
−3: Chandra, Torch of Defiance deals 4 damage to target creature.
−7: You get an emblem with "Whenever you cast a spell, this emblem deals 5 damage to any target."

Buy This Card! https://shop.tcgplayer.com/magic/kaladesh/chandra-torch-of-defiance

Woe Strider

Color Identity:B

Market Price: $1.25

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/206627_200w.jpg

When Woe Strider enters the battlefield, create a 0/1 white Goat creature token.
Sacrifice another creature: Scry 1.
Escape—{3}{B}{B}, Exile four other cards from your graveyard. (You may cast this card from your graveyard for its escape cost.)
Woe Strider escapes with two +1/+1 counters on it.

Buy This Card! https://shop.tcgplayer.com/magic/theros-beyond-death/woe-strider

Siege-Gang Commander

Color Identity:R

Market Price: $0.82

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/162180_200w.jpg

When Siege-Gang Commander enters the battlefield, create three 1/1 red Goblin creature tokens.
{1}{R}, Sacrifice a Goblin: Siege-Gang Commander deals 2 damage to any target.

Buy This Card! https://shop.tcgplayer.com/magic/dominaria/siege-gang-commander

Mayhem Devil

Color Identity:B,R

Market Price: $0.41

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/188173_200w.jpg

Whenever a player sacrifices a permanent, Mayhem Devil deals 1 damage to any target.

Buy This Card! https://shop.tcgplayer.com/magic/war-of-the-spark/mayhem-devil

Castle Locthwain

Color Identity:B

Market Price: $2.65

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/199388_200w.jpg

Castle Locthwain enters the battlefield tapped unless you control a Swamp.
{T}: Add {B}.
{1}{B}{B}, {T}: Draw a card, then you lose life equal to the number of cards in your hand.

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

Lazotep Reaver

Color Identity:B

Market Price: $0.10

ImageURL: https://tcgplayer-cdn.tcgplayer.com/product/187251_200w.jpg

When Lazotep Reaver enters the battlefield, amass 1. (Put a +1/+1 counter on an Army you control. If you don't control one, create a 0/0 black Zombie Army creature token first.)

Buy This Card! https://shop.tcgplayer.com/magic/war-of-the-spark/lazotep-reaver

Turning Yasharn, Implacable Earth or Nissa, Who Shakes the World into a Cauldron Familiar is a pretty big deal. Getting a full playset of Siege Gang Commander into play isn't bad either. You do lose access to Gilded Goose and Collected Company in Grixis, but you also gain access to Aether Gust and Mystical Dispute. With the printing of the final four pathways the mana has improved significantly even though Grixis lacks a fastland. 

Kaldheim looks really good. Killer flavor, interesting new designs, and some very powerful new cards for Standard. Keep an eye out for my usual 50 decks coming soon™!