Companion — Your starting deck contains only cards with even mana values. (If this card is your chosen companion, you may put it into your hand from outside the game for as a sorcery.)
When Gyruda enters, each player mills four cards. Put a creature card with an even mana value from among the milled cards onto the battlefield under your control.
Gyruda cheats big even-costed creatures into play by milling and reanimating, then loops via blink and reanimation to repeat the trigger and snowball a board (or assemble a combo). Early turns ramp and set up graveyard/blink engines; mid-game Gyruda enters, steals or returns a fatty, and you chain effects until the board breaks open.
Free reanimation on a stick that steals creatures from any player's mill, including opponents'
Built-in deckbuilding payoff—an even-only deck still packs powerful clones, reanimators, and control pieces
Supports a hard infinite combo with Clever Impersonator/Spark Double-style clones plus a sac/blink outlet
Dimir gives premium interaction, card advantage, and tutors
Even-mana value recursion to rebuy wipes, removal, and combo pieces from the yard.
Lean into a tight clone-loop combo line (Spark Double or Phantasmal Image + a free blink/sac outlet) backed by Thassa's Oracle as a clean finisher to win without a long board stall. Maximize even-cost ramp (Arcane Signet, Coalition Relic, Hedron Archive) and even-cost tutors/recursion to find and protect Gyruda faster, and add resilient blink enablers like Conjurer's Closet and Deadeye Navigator. Round out with the best even-mana Dimir interaction and graveyard insurance so a single exile effect doesn't end your game.
Legendary Creature — Demon Kraken
as a sorcery.)