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.
This has happened to me too. I used Elemental Hero Neos and Gate Guardian for Neos Knight, and I intended on using de-fusion to split them up when the player I was against used enemy controller. De-fusion simply sent Neos Knight to the extra deck, without bringing any of them back from the graveyard. It definitely seems bugged.
All materials need to be in the graveyard and they need be able to be special summoned from there, if one of those materials aren't in the graveyard or cannot be special summoned, so none is special summoned. In Emma's case, Gate Guardian cannot be special summoned unless it was special summoned firt by its own method and was sent from the field to the Graveyard.
3 monster spaces, 5 monsters.. what did you expect?
Is this card bugged ... I fusion summoned "Twin Headed Thunder Dragon" using 2 Thunder Dragons ... and I attacked with the fusion monster then I used Defusion to bring the 2 thunder dragons from th GY ... It returned the fusion monster without summoning any of its materials that were in GY so Is this right ... I did not use any substitute !!!! What is that !!!
No No ... I remembered ... I was using fusion recycling plant and returned one of the two materials to hand (Note : There was a third thunder dragon at GY that was not used as a mat.) ... My bad .. You can only summon the monsters that were used exactly for fusion summoning even if You have many copies of the material monsters in the GY IT won't work
I used it for Neos Knight by fusing Neos and EHero Blazeman, I took out some monsters in the battle phase with Neos Knight and then tried to use DeFusion to special summon Neos and Blazeman and it didn't, it just returned Neos Knight to the Extra deck