Fusion Monster

Fusion Monsters, colored violet, are cards representing a combination of two or more monsters. Fusion Monsters may only be included in the Extra Deck, and cannot exist in the hand or Main Deck. If a Fusion Monster is returned to its owner's hand or Deck, it is instead sent back to the Extra Deck. However, they may be sent to the Graveyard when destroyed, as well as removed from play. In the anime, the original didn't use them a lot. In Yu-Gi-Oh GX, however, introduced many fusion cards and many powerful fusion monsters were released during this time. In Yu-Gi-Oh 5D's Synchro Monsters appear to have filled this position.

Originally, the only way to properly summon a Fusion Monster was through a Fusion Summon involving the required cards as well as Polymerization. Monsters used with Polymerization are called Fusion Material Monsters.

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 returned from the Graveyard to the field, it must be Fusion Summoned properly.

There are some Fusion Monsters that have special Summoning Conditions. For example, the Elemental Hero Fusion Monsters have a clause stipulating that they may not be Special Summoned unless they are being Fusion Summoned. This also rules them out from being Special Summoned either from the Graveyard or when removed from play. Others may disallow the use of Fusion Substitute Material Monsters, and in even rarer cases, both of these conditions may be applied, such as in Rainbow Neos.

Fusion Monsters even have their own Equip Spell Card: Fusion Weapon

There are a few ways to properly Fusion Summon a Fusion Monster:
 * Chain Material
 * Cyberdark Impact!
 * Dragon's Mirror
 * Dark Fusion
 * Dark Calling
 * Fusion Gate
 * Future Fusion
 * Instant Fusion
 * Miracle Fusion
 * Overload Fusion
 * Polymerization
 * Power Bond
 * Super Polymerization
 * Vehicroid Connection Zone
 * Fossil Fusion
 * Miracle Contact

And a few ways to Special Summon a Fusion monster:
 * Cyber-Stein
 * Magical Scientist
 * Metamorphosis
 * Re-Fusion
 * NEX
 * Summoner of Illusions
 * The VWXYZ Series and Armityle the Chaos Phantom "Union Fusion"
 * The Elemental Hero Neos and Gladiator Beast also Chimeratech Fortress Dragon Fusions "Contact Fusion"
 * The "Hex-Sealed Fusion" Monster Cards (The Earth - Hex-Sealed Fusion, The Dark - Hex-Sealed Fusion, The Light - Hex-Sealed Fusion)

1 Fusion Material Monster can be replaced by Fusion Substitute Monsters in Fusion Summons with cards that either do not specifically state the monster to be used as a Fusion Material Monster, or do not have a summon condition that limits either what monsters may be used for the Fusion Summon, or in what way it may be summoned.

Most Fusion Monsters need two Fusion Material monsters, and then the Polymerization card. However, certain Fusion Monsters can be summoned out of the Extra Deck via a process known as Contact Fusion, which requires no Polymerization.