Worldgorger Dragon

It is possible for Worldgorger Dragon to leave the battlefield before its “enters the battlefield” trigger resolves. If this happens, then the “leaves the battlefield” trigger will have nothing to return. Then its “enters the battlefield” trigger resolves, and all other permanents you control are exiled forever.

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 doesn’t have to go back to the same place. It can’t enter the battlefield enchanting a permanent that enters the battlefield at the same time.

If Animate Dead is put onto the battlefield enchanting Worldgorger Dragon, Worldgorger Dragon’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 you’d like. If you can’t choose a different card, and no player chooses to break the loop, the game ends in a draw.

If Worldgorger Dragon leaves the battlefield before its enters-the-battlefield ability resolves, the "leaves-the-battlefield" ability will trigger and resolve first. It won't return anything. Then the enters-the-battlefield ability will exile all other permanents you control indefinitely.

If an Aura is exiled with Worldgorger Dragon and then returns to the battlefield, the player who controls the Aura as it enters the battlefield chooses what it will enchant. An Aura put onto the battlefield this way doesn't target anything (so it could be attached to an opponent's permanent with hexproof, for example), but the Aura's enchant ability restricts what it can be attached to. If the Aura can't legally be attached to anything, it stays exiled. It can't enter the battlefield enchanting a permanent that enters the battlefield at the same time.