Target 1 Fusion Monster on the field; return that target to the Extra Deck, then, if all the Fusion Material Monsters that were used for its Fusion Summon are in your Graveyard, you can Special Summon all of them.
These are the Cards that can Fusion Summon a Monster. You can then use De-Fusion after you attack with the Fusion Monster to Special Summon the Fusion Material Monsters since it's a Quick-Play Spell Card. You can then attack using those Special Summoned monsters for potential OTK.
Wait... does this card text means if its your opponents fusion monster, since the materials arent in your graveyard, it just acts as a hane hane quickplay spell? Thats pretty busted if fusions become meta