Arm with Aether

Oracle Text

Until end of turn, creatures you control gain "Whenever this creature deals damage to an opponent, you may return target creature that player controls to its owner's hand."

Card Rulings

6/1/2011 Only creatures you control on the battlefield when Arm with Aether resolves gain the ability. Creatures you gain control of later in the turn won’t be affected.
6/1/2011 The affected creatures keep the ability even if another player gains control of them that turn. If such a creature deals damage to you, the ability will trigger, targeting a creature you control.
6/1/2011 The granted ability triggers on all damage dealt by the creature to one of your opponents, not just combat damage.
6/1/2011 In a multiplayer game, if an affected creature deals damage to two of your opponents simultaneously, the ability will trigger twice.