Fusion Monster
Fusion Monster Cards can only be included in the Fusion Deck. They cannot exist as part of the Main Deck, however, they can still go to the Graveyard when destroyed, and they can still be Removed from Play.
There are a few ways to summon a Fusion Monster:
Using Polymerization is the only way for a Fusion Monster to be Fusion Summoned to the field, unless a card like Fusion Gate is in play. Monsters Tributed with Polymerization are called Fusion-Material Monsters.
When a Fusion Monster is returned to it's owners hand, it is instead sent back to the Fusion Deck, since a Fusion Monster cannot exist either in the Hand or Deck.
If a Fusion Monster is Special Summoned to the field via a Card, such as Metamorphosis, and then sent to the Graveyard, it cannot be Special Summoned to the field from the Graveyard with cards such as Premature Burial, Call of the Haunted, or Monster Reborn. In order for a Fusion Monster to be resurrected from the Graveyard, it must be Fusion Summoned properly with Polymerization, or with the effect of Fusion Gate.
