You choose which mode you're using as you put the ability on the stack, after the creature has entered the battlefield. Once you've chosen a mode, you can't change that mode even if the creature leaves the battlefield in response to that ability.
24-11-2014
wotc
If a mode requires a target and there are no legal targets available, that mode can't be chosen. You must choose another mode if able.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.
Craig J Spearing2015-01-23
