Tidespout Tyrant

The bounce-on-cast trigger turns a control deck's natural rhythm into a soft lock. Every spell you cast, including the cheap cantrips that refill your hand, returns a permanent to its owner's hand: point the trigger at your opponent's board and a low-curve flurry of small spells dismantles their battlefield one permanent at a time, but point it at your own enters-the-battlefield creatures and the same engine becomes a value loop. The interaction that made it famous is mana-positive bounce: aim the trigger at a rock that taps for more than it costs to recast (the Sol Ring and Mana Crypt class of artifact), pair it with a cheap spell to recur, and the loop generates mana, draws and clears the table on every iteration until your opponent has no permanents left. None of that is on the card; the card just says you bounce something whenever you cast. What the design recognizes is that "whenever you cast a spell" is one of the most repeatable triggers in the game, and stapling permanent bounce to it rewards the deck that was already going to cast a lot of cheap things. The eight-mana, triple-blue cost is the brake: this is a payoff you earn after assembling the engine, a 5/5 flier that wants you to already have a hand full of spells and a plan for what to do once the table is empty.