Tidebinder Mage

A hatebear with a hyperspecific menu, and the narrowness is the whole design. The tap-and-lock fires only at red or green creatures, which makes this less a generic Merfolk body than a color-keyed wrench: useless against blue mirrors, devastating against the aggressive red and green decks it was tuned to punish. The lock is the clever part. It is not a one-shot tap but a persistent leash, holding the target down for as long as you control this creature, which turns a 2/2 into a soft removal spell that neutralizes a bigger threat for as long as it survives. That conditionality runs both ways: bounce it, kill it, or steal it, and the locked creature springs back to life, so the effect carries a built-in fragility that a hard answer never would. The targeting clause also does quiet work by reading "tap target," meaning it can catch an already-summoning-sick creature and simply keep it tapped, denying a blocker or a fresh attacker before it ever swings. The disruption rides on a maindeckable body rather than a dedicated answer: a 2/2 you would run anyway that happens to read your opponent's board and clamp down on the one creature that matters. Against the right two colors it is among the most efficient disruptive two-drops blue has had; against the other three it is a 2/2 with nothing to tap.