Aether Tradewinds

The symmetry is mandatory, and that is the whole tension. You cannot point both halves at your opponent; one return has to hit a permanent you control, which converts what would otherwise be a clean two-mana bounce into a three-mana spell that taxes your own board. Unconditional single-target bounce runs two mana (Boomerang, Unsummon-adjacent rates), so the extra mana and the forced self-target are the price for getting two returns on one card. To one deck that price is dead weight: a tempo player ahead on board treats bouncing their own permanent as collateral damage on an overcosted removal spell. To another it is the entire point. In a shell built on enters-the-battlefield triggers, returning your own creature is the reason to cast the card, and the opponent's permanent leaving is the free rider. Instant speed lets both readings breathe: you can rescue your own permanent from a removal spell in response while stripping a blocker, or wait until the end of an opponent's turn to reset their land or planeswalker and rebuy a value creature on the way. The card never resolves the tempo-versus-value question for you; you resolve it by choosing what each half points at. That is why it reads as filler in a deck with nothing worth bouncing and as infrastructure in a deck whose permanents would rather start over.