When Fiend Hunter enters the battlefield, you may exile another target creature.
When Fiend Hunter leaves the battlefield, return the exiled card to the battlefield under its owner's control.
3/16/2018 If Fiend Hunter leaves the battlefield before its first ability has resolved, its second ability will trigger and do nothing. Then its first ability will resolve and exile the targeted creature indefinitely.
3/16/2018 Once the exiled permanent returns, it’s considered a new object with no relation to the object that it was. Auras attached to the exiled permanent will be put into their owners’ graveyards. Equipment attached to the exiled permanent will become unattached and remain on the battlefield. Any counters on the exiled permanent will cease to exist.
3/16/2018 If a token is exiled this way, it won’t return to the battlefield.