Gombli, Wish-Giver

{x}{g/w}, {ut}: You gain X life.
When Gombli enters the battlefield, you may
search your library for a card and exile it
face-down, then shuffle your library.
Whenever Gombli becomes the target of a
spell or ability an opponent controls, you
may exile Gombli and cast the face-down card
without paying its mana cost.