Disappear

Repeatable bounce, packaged as an Aura rather than a spell. Most blue tempo of its era paid full price every time to send a creature back to hand; this attaches once and then asks only a single blue pip to return both itself and the enchanted creature. That structure works two directions. Hung on an opponent's threat, the activation is dirt cheap, but the bounce drags the Aura along with it: to re-establish the soft lock you have to recast Disappear at four mana before you can tax their next deployment, so the loop is real but the upkeep is steep, never free. Hung on your own creature, it becomes a reusable rescue-and-replay button, ducking removal or re-triggering an enters-the-battlefield ability at instant speed for the cost of redeploying both halves. The self-return is what stops the engine from running away: every use is a full reset, paid in tempo and re-attachment rather than just the blue mana. The wider idea it embodies is that an Aura need not be a static buff. It can be a portable piece of interaction that sits on the battlefield until you choose to spend it, and the recurring four-mana re-attachment is the tax built into doing so.