River Sneak

Unblockability is what turns this from a cute board-development creature into a genuine clock. A 1/1 that grows whenever another Merfolk lands beside it is fine on its own, but pin that pump trigger to a body the opponent cannot interact with in combat and the math gets ugly fast: every Merfolk you deploy after this one feeds it, and because the damage cannot be chumped or stopped at the gate, each follow-up stacks another point of committed, unanswerable damage that turn. The bonuses live entirely on tempo and vanish at end of turn, which pins the card firmly to the fast side of the tribe. This is a creature that wants the rest of the hand to spill out behind it on the same turns it attacks, not a value engine that accrues over a long game. That ties it to the wide, aggressive end of Merfolk strategies, where evasion separates a tribe that swarms from one that actually closes. Its role is to receive a tribe's momentum: the lane that converts a flooded board into lethal before the opponent stabilizes, asking nothing in deckbuilding except more of the same creature type pointed the same direction.