Whenever Galepowder Mage attacks, exile another target creature. Return that card to the battlefield under its owner's control at the beginning of the next end step.
Galepowder Mage’s ability can target a creature controlled by any player. It’s not optional.
The exiled card will be returned to the battlefield at the beginning of the end step even if Galepowder Mage is no longer on the battlefield at that time.
If Galepowder Mage is the only creature on the battlefield when it attacks, its ability has no effect.