Make big Hydras, then proliferate the hell out of them and then smash. Well, that's the general gist of the deck.
With the recent debut of Zaxara, the Exemplary in the 2020 Commander precon, Hydra Tribal in EDH now has an actual viable commander for the deck. Zaxara has everything a Hydra deck wants. She's a legendary Hydra, she makes mana for Hydras, and she even gives you a Hydra friend whenever you cast a spell with X in the mana cost, which basically covers most hydras in the game.
WINCONS
Now, what you'd typically think of Hydras in Magic are these huge creatures with so many +1/+1 counters on them. Our primary win condition is to slam into our opponents with so many hydras, preferably with unblockable, flying, or trampling hydras. Literally anything goes when it comes to hydras.
However, should the combat route not work out, we have two more win conditions. One is Altar of Dementia. Now you might be thinking, how does Altar of Dementia work in this deck? It's simple really. If you have a number of huge hydras but no way to punch through to an opponent, just throw them into the altar and mill them out. Granted, it's not very reliable but it works.
The other win condition is even less reliable, but it works. Phyrexian Hydra is the only Hydra with the infect mechanic and normally, you'd be one-shotting people with this creature. However, we have proliferation on our side. Contagion Clasp, Contagion Engine, Sword of Truth and Justice, Inexorable Tide. All of these can help proliferate our hydras to absolutely gigantic sizes, which in turn helps with all of our win conditions.
MANA BASE
The mana base for the deck is relatively decent, not too expensive and relatively easy to obtain. Guildgates, temples, and checklands are our main duals. But we also use lands that tap for more than one mana. Urborg+Coffers is a tried and true combo, Ancient Tomb is always good, and Temple of the False God does a reasonable impression of Ancient Tomb if we can get to more than 5 lands, which shouldn't be too difficult. The ramp package is what you'd normally see in a deck with green. Farseek, Growth Spiral, Crop Rotation, Skyshroud Claim, Circuitous Route, Cultivate, Kodama's Reach, and Tempt with Discovery all help us to ramp, and to find our most powerful lands to slam down our biggest creatures. Sol Ring and Commander's Sphere are our only mana rocks in the deck, though an argument could be made for more.
There's another category to this, namely mana-sinks and mana multipliers. Nyxbloom Ancient gives us so much mana, provided you can stick it and it lives. Kruphix, God of Horizons and Omnath, Locus of Mana both help us bank the mana for bigger hydras, and Wilderness Reclamation keeps up the illusion of us being a control deck, when in fact we have very little control elements.
CARD DRAW/TUTORS
Colossal Majesty is one of our main sources of card draw. Despite being in Sultai colors, we have very little in the way of countermagic or card draw spells, so most of our card draw will have to be creature-based. Hydroid Krasis, Consecrated Sphinx, and Yawgmoth, Thran Physician all work very well to help us draw cards. Kiora, Behemoth Beckoner is another source of card draw, triggering whenever a creature with power 4 or greater enters the battlefield.
As for tutors, we run only 2 artifact tutors. Treasure Mage and Tribute Mage find our primary win condition artifacts, with Tribute Mage able to fetch Lightning Greaves, Altar of Dementia, and Contagion Clasp. Tamiyo, Collector of Tales also helps us dig for the pieces we need to either start our domination or finish the game.
One of our biggest tutors also serves as a win condition of its own. Emergent Ultimatum, a 7-mana sorcery from the new Ikoria set, can win us games, provided we tutor for all the right pieces that force our opponents into a catch-22 situation. One possible Ultimatum package is Herald of Secret Streams/In Garruk's Wake/Biogenic Upgrade. This allows us to wipe any opposing boards and clear the way for the hydras to crash through, with the possibility of making them bigger. Final Parting feeds into two categories, namely tutoring for what we need and putting something we can use later into the graveyard.
COUNTERS
As mentioned earlier, proliferate is one source of our counters. However, we will need more, both to be redundant and to always have one on hand. Hadana's Climb, Hydra's Growth, and Biogenic Upgrade all aid us in making our monsters grow.
REMOVAL/BOARD CONTROL
We have 2 major boardwipes in the deck. Damnation helps us to wipe the board clean should we ever fall behind. In Garruk's Wake helps us to clear the way for our hydras to swing in and start killing people. Assassin's Trophy, Deathsprout, Krosan Grip, and Putrefy all help with dealing with troublesome permanents. Even with all of this, most of our removal is creature-based, aka slamming into their creatures with ours. Gargos, Vicious Watcher, Voracious Hydra, and Polukranos, Unchained all put their bodies to good use and get rid of blockers before we can start swinging in.
THE GRAVEYARD
We don't have much in the way of recursion. Only Seasons Past, Mythos of Brokkos, and Once and Future help us with getting back key cards from the bin, namely our proliferate engines and things that either give haste or enable evasion. Final Parting and Mythos of Brokkos both serve to put key pieces into the bin in order for us to fetch them later with the mythos itself, or Seasons Past.
