2017-03-14 : Craterhoof Behemoth’s triggered ability affects only creatures you control at the time it resolves. It won’t affect creatures that come under your control later in the turn.

2017-03-14 : The value of X is determined only as Craterhoof Behemoth’s triggered ability resolves, potentially including Craterhoof Behemoth itself. It won’t change later in the turn if the number of creatures you control changes.