Kiora, Sovereign of the Deep

The payoff answers the classic problem with sea-monster tribal: the creatures cost too much to reliably chain into one another. Cast a Kraken, Leviathan, Octopus, or Serpent from your hand and you dig X deep, where X is that spell's mana value, then deploy something smaller for free. The elegance is in the cascading value curve it implies: a high-cost serpent opens a wide window and pulls out a mid-range body underneath it. The design caps the free spell below the trigger's mana value, so you are always trading down, never looping the same fatty back for nothing. Just as important, the free cast comes off the library, not the hand, so it does not re-trigger the ability itself; the engine advances in single, decreasing steps rather than snowballing out of one top-heavy draw. The dig also keys off the spell's printed mana value rather than what you paid, meaning cost reducers cheapen the cast without shrinking the window they open. The 4/5 with vigilance and ward attends to the awkward truth that most payoffs of this shape die before they generate value: it can attack, block, and hold up the reveal in the same turn, and the ward tax makes cheap removal a poor trade. This is a Simic engine that rewards raw mana investment over clever sequencing, a rare kind of payoff that gets better the more expensive your creatures are.