Genesis Hydra

The elegance is that X does triple duty from a single number: it sets the body, it sets how deep you reveal, and it caps what you can pull from that reveal, all decided on cast. Pour in seven and you look at seven cards, drop a nonland permanent of mana value seven or less onto the battlefield for free, and the Hydra still arrives sized to match. The cast trigger is the part worth dwelling on, because it goes on the stack separately from the creature and resolves on its own terms: even if the Hydra spell gets countered, the trigger stays on the stack and still resolves, so the dig happens and the permanent lands regardless of whether the fatty ever hits the battlefield. That makes it a hit-on-the-stack value play wearing a fatty's clothes, and it rewards a deck stacked with high-impact nonland permanents rather than the random top-deck a blind reveal usually represents. The deckbuilding tension runs opposite to intuition: the bigger you cast it, the deeper you see, the more you can put down, and the better your odds that a card genuinely worth keeping sits in the reveal, since you only ever keep one. It belongs to a green tradition of mana-as-card-advantage payoffs, the line built to convert a flooded board into bodies and spells at once. The floor, though, is real: cast it for zero and you reveal nothing, the Hydra enters with no counters, and the state-based check kills it before it does a thing. Commit meaningful mana or get nothing at all.