Send, from your side of the field to the Graveyard, the Fusion Material Monsters that are listed on a "Gem-Knight" Fusion Monster Card, then Special Summon that Fusion Monster from your Extra Deck. (This Special Summon is treated as a Fusion Summon.) When you do: Banish this card from the Graveyard to target 1 "Gem-Knight" Fusion Material Monster used for the Fusion Summon; the Fusion Summoned monster gains that monster's ATK until the End Phase.
How to Get
Sends from your field to your Graveyard / Activates from your Graveyard / Fuses Materials from your field
Banishes itself from Graveyard for cost
Fusion Summons / Special Summons from your Extra Deck