Will-o-the-Wisp

When Will-o-the-Wisp enters the battlefield,
exile up to one target nonland, nontoken
permanent you don't control with mana value 4
or less.
When Will-o-the-Wisp leaves the battlefield, the
exiled card's owner creates an X/X blue Illusion creature token, where X is the mana value of the
exiled card.