I love a good tribal legend. Tribes are a great way to introduce new players to building Commander decks. A big issue when introducing new players to deckbuilding in Commander is the overwhelming number of options! With a format as wide as Commander is, giving a new player the focus of a tribal build reduces the card pool to something that can be more manageable.
Unesh, Criosphinx Sovereign (aka "Leon") brings this together in a wonderful way. If you are using Leon as your commander, you have 28 Sphinx options to add to your deck. You aren't going to add all of them, so actual number of tribal creatures in your deck is going to be less than that. This means that, unlike Goblins, Zombies, Elves and the other major tribes, you are going to have to step beyond just the tribe to get what you need. This gives the new player some direction, and some freedom to add pet cards and fill in problem areas in your deck.
It also works well for me! Sphinx tribal comes with a set of problems that you see with tribes that have minimal support and tend to be more costly than the successful tribes. I do love a good challenge!
If we've decided to start with Unesh, Criosphinx Sovereign, then it is best to look carefully at every part of the card to determine what we're working with.
Casting Cost. We are running a commander that costs six mana. This means that you probably aren't going to get to recast Leon too many times. It wouldn't take long for Leon to cost 10 mana. Once it costs that much, is saving two mana for a Sphinx really that great? This tells us that we are likely looking at ways to make Leon (and as many other spells as possible) cheaper, and adding plenty of mana ramp to the deck. We are also going to be looking for ways to protect Leon once it hits the battlefield. The best way to keep the cost to recast Leon down is to prevent having to recast it altogether.
Flying and 4/4. Unesh can do combat! With evasion and a large body in the air, Leon can hit for combat damage. While I don't think I want to build a deck around Leon winning with combat damage, it is certainly an option few opponents will be watching for. With the tribal abilities Leon brings, everyone is expecting Sphinx tribal. Sphinx are a bigger tribe, so beating down with Leon and the rest of the tribe is certainly an option too.
Abilities. This is why we're here. The abilities make casting a Sphinx cheaper and lets you draw cards when they enter the battlefield. With enough Sphinx in the deck, you should expect to see a hand full of cards for most of the game.
Sphinx. They are going to be two less to cast and offer up four-card versions of Fact or Fiction whenever they enter the battlefield. Fact or Fiction is a solid card in regular one-on-one games, but in multiplayer games it just gets better. You are choosing who makes the piles of cards for you. Think of all the times when you are working with one of the players in the game to take down another player. Every time that happens, you are essentially asking a teammate to split the piles for you to choose. In these situations you are likely going to see a pile of four cards and a pile of zero cards. I have done this multiple times in my games, knowing that player is not going to use those cards against me, but against another player. Even forgetting those instances, and assuming your opponent is trying to make this as difficult as possible, you are either getting the exact card you want from the top four cards, or a stack of cards to add to your hand. This is an all-upside ability!
In addition to Sphinx, I want to add some Shapeshifters to the deck. They can cost less and give us some creatures to play in the early game, since most Sphinx cost five or six mana and we don't want to wait that long to start dropping creatures. Two interesting Shapeshifters are a couple of tribal instants, Ego Erasure and Wings of Velis Vel. They count as Sphinx when they are cast, so they get even cheaper and also get us the mini-Fact or Fiction in addition to their abilities. Drawing cards at instant speed is also a good thing, so I was happy to add them in as well.
As long as we are going tribal, adding cards that help our Sphinx theme along just makes sense. We'll add a few cards that pump power and toughness. We probably don't need many of these since Sphinxes are already big, but a Door of Destinies can add a little more, making an attack from even two Sphinxes hit for over 10 damage. That's enough to make most players sit up and take notice!
I've also added ways to make Sphinx Tokens. Volrath's Laboratory and Riptide Replicator aren't offering particularly good deals for Sphinx Tokens, but it does activate the mini-Fact from Leon when the tokens hit, so they are in.
I've also added Deadeye Navigator to the deck. With every Sphinx offering an enters-the-battlefield effect, Deadeye Navigator lets you get that option for only two mana. The card is ubiquitous in blue decks and I'm tired of seeing it all the time, but it is going to be just too good in this deck not to run it.
Cost. Making Sphinxes cheaper was one of the goals, so I added a few cards that can do that for us. With a theme deck, Belbe's Portal is always fun, letting you get a Sphinx onto the battlefield for only three mana! Urza's Incubator just reduces the cost, so later in the game when you have plenty of mana, you'll be able to cast multiple Sphinxes in one turn!
No real reason to stop there, though. Planar Gate and Sapphire Medallion reduce the costs of all your spells, while Warden of Evos Isle will be a bird that brings the Sphinx beatdown just a little faster.
Protection. The package includes the standard equipment that end up in a lot of Commander decks that want to keep the commander in play: Lightning Greaves, Swiftfoot Boots, et al. The joy of blue lies with all the counterspells you can include. This means that while the cards are there primarily to protect Unesh, a counter is always handy when other things are going downhill fast.
Ramp. With a deck like this, ramp is going to be essential. While the card draw you'll be generating with Leon's mini-Fact will help, it won't be doing much until you can actually cast Leon. With mana rocks and some early creatures that can tap for mana, you should be able to get out to a reasonable start.
This brings us to the deck itself.
This is a skeleton of a deck and I don't recommend playing it. Treat this deck as a list of ideas for your Unesh deck, as opposed to a fully fleshed-out deck that you can copy and run with your friends as soon as Hour of Devastation comes out There isn't nearly enough removal for my liking. It also seems insane to be running a blue deck but have so few instants and sorceries. Perhaps your metagame will let you get away with a slim removal package, but I find few do. I also want to see more early defense. Whether that comes with a creature package that costs less than four mana to cast, or cards that set up a pillow fort defense, the deck will need something.
Another option is a graveyard recursion package. With all these mini-Facts going off, your graveyard will likely hold a trove of cards you'd love to have at some point in the game. Graveyard recursion in blue isn't easy, but if you bend your deck more towards artifacts, that would certainly help things along.
All of this will likely need to come at the cost of reducing the Sphinxes in the deck and I don't want to be the one to do that for you. While I did drop a few to try and set up this deck, the real cuts should be your own. With a curve this high, something needs to give. I left it as big as it is because I liked the idea that you would likely find another Sphinx to cast with every mini-Fact you used. However, loading your deck with over 20 creatures that cost five or more to cast is a dangerous game, even in Commander.
Finding other versions of Unesh to help you along a little further, you might want to try decklists of other blue commanders that do something similar. Arcanis the Omnipotent is another expensive blue commander whose ability draws you cards, so the cards you find in Arcanis decks may also apply to Leon. Looking at other theme decks will also help you find cards to further your theme. Sygg, River Guide decks can offer some interesting options when looking at themes.
I think Unesh, Criosphinx Sovereign can be a great build for newer Commander players, while offering interesting challenges to the more experienced Commander crowd!