Wormfang Crab

The whole Wormfang cycle ran on one uncomfortable premise: each creature exiled something of yours on entry and returned it only when the creature left, a self-imposed loan that lasts as long as the body does. Most of them set the terms themselves, exiling your own creatures or a fixed handful of cards. This one hands the steering wheel to your opponent and points it at any permanent you control other than the Crab. That distinction is the whole problem. The opponent will never exile the permanent you want gone; they take the one that hurts most, your best enchantment, your only blocker, a land you cannot spare. The choice is adversarial by construction, so the dream of looping a value permanent in and out almost never materializes: the only board state that forces a friendly choice is the one where you control exactly one other permanent, and a player rarely casts a four-drop into that. The leaves-the-battlefield return is the trap the design sets. It reads as a free flicker outlet, but with your opponent picking the permanent, it is just a deferred refund on a permanent you never wanted to surrender.

So the unblockable 3/6 is the actual product, and the exile is the tax stapled to it. It is a clock that pushes damage through regardless of the board, paid for with a hostage you do not get to choose.