When Nulltread Gargantuan enters the battlefield, put a creature you control on top of its owner's library.
5/1/2009 Nulltread Gargantuan’s ability doesn’t target the creature you put on top of its owner’s library. You don’t choose one until the ability resolves. No one can respond to the choice.
5/1/2009 If you control no other creatures, you’ll have to put Nulltread Gargantuan on top of its owner’s library.