Creature â Nightmare Dragon
When Worldgorger Dragon enters the battlefield, exile all other permanents you control.
When Worldgorger Dragon leaves the battlefield, return the exiled cards to the battlefield under their owners' control.
It is possible for Worldgorger Dragon to leave the battlefield before its â€œenters the battlefieldâ€ trigger resolves. If this happens, then the â€œleaves the battlefieldâ€ trigger will have nothing to return. Then its â€œenters the battlefieldâ€ trigger resolves, and all other permanents you control are exiled forever.
If Animate Dead is put onto the battlefield enchanting Worldgorger Dragon, Worldgorger Dragonâ€™s enters-the-battlefield trigger will exile Animate Dead, which causes you to sacrifice Worldgorger Dragon, which causes Animate Dead to return to the battlefield attached to a creature card in a graveyard of your choice. If you can choose a creature card other than Worldgorger Dragon, you must do so after as many iterations of this loop as youâ€™d like. If you canâ€™t choose a different card, and no player chooses to break the loop, the game ends in a draw.
If an Aura is exiled with Worldgorger Dragon, the player who controls the Aura when it enters the battlefield chooses what it will enchant. It doesnâ€™t have to go back to the same place. It canâ€™t enter the battlefield enchanting a permanent that enters the battlefield at the same time.