Mark of Eviction
Most blue bounce spends itself once and goes to the graveyard; this Aura keeps coming back. Because the Mark is an Aura on the creature it returns, the upkeep trigger sends both the creature and the Mark to their owners' hands at the same time, so you reattach it next turn and do it again. The recursion is free in card terms: you spend a blue each cycle to recast the same Aura, never burning a card off your stack to do it. The payoff is repeated tempo at the opponent's expense. Pay one mana, force them to replay a more expensive creature; the math runs in your favor every loop, and any enters-the-battlefield trigger they have re-fires alongside it, which is the cost that points it at creatures whose ETB you do not mind seeing twice. The timing is the soft spot. The bounce happens during your upkeep, after the creature has already untapped and attacked, so it is a delayed lock rather than an instant-speed answer. The clause that does the heavy lifting is the second one: returning every Aura riding on the creature lets a single trigger strip a stack of buffs or peel another player's enchantments off in one motion, undoing investment the opponent has to pay for again. This reads as an early attempt to stretch one-shot blue bounce into a recurring engine, with the self-return built in so the door never quite latches.
