Watertrap Weaver

The enters-tap effect dressed up as soft removal. Tapping an opposing creature and denying it the next untap step buys exactly one full turn of immunity: the blocker is gone for your attack, the attacker is gone for your defense, and then it comes right back. That single-turn window is the whole transaction, which is why the 2/2 Merfolk body earns its keep as much as the trigger does. The creature stays on the battlefield doing tempo work after the tap-down resolves, and the trigger keys off entering, so any way to flicker or rebuy the body re-aims the lock at a fresh target. This is blue tempo at its most literal: it does not kill anything, it does not even keep the target tapped indefinitely, it just steals a beat in a race where a single beat decides combat math. The design discipline is the one-step duration. A permanent tap would be removal in disguise; tapping forever would warp board states. Holding the creature down for precisely one untap step keeps the card a tempo play rather than an answer, the kind of effect that wins on the back of a clock rather than on attrition.