Temporal Adept

Boomerang stapled to a body, with the wrinkle that the body costs almost as much to fire as the spell ever did. The activation is the whole story: three blue pips plus a tap to bounce any permanent, repeatable every untap you keep this 1/1 alive. That triple-blue tax is what holds a recurring Boomerang in check; every turn you spend it is a turn you spend nothing else, so the lock is only as good as the manabase feeding it. Aim the activation at an opponent's land and you build a soft prison against a board that can never quite assemble; aim it at your own creature or enchantment with a useful enter-the-battlefield trigger and you have a value engine that never empties. The flaw is structural and plain: a 1/1 that must survive to your next untap dies to any incidental burn or attacker, and it does nothing to the board the moment it resolves. Every bit of its power is deferred to the turn after, and then the turn after that. What it rewards is a deck willing to warp its color base toward triple-blue, and what it pays back is a grinding, attrition-flavored win condition: not a fast kill, but a patient refusal to let the opponent ever keep a permanent on the table.