Fusion Keyword

Fusion: X, Y (When a card with the Fusion
keyword enters the battlefield find one instance
of the cards named X and Y starting with the
battlefield, followed by your hand, followed by
the graveyard, followed by your library. Once
you find one instance each of card X and Y by
this method, exile them. When the Fusion card
leaves the battlefield, summon cards X and Y
to the battlefield)