As it is a card to bring out My Evil Pony Fusion Monsters, it's only fitting that the artwork be a sort of corrupted form of the original fusion card. The card's info says:
Rainbow Fusion
Normal Spell
Send from your hand or field to the Graveyard the Fusion Material Monsters listed in a "My Evil Pony" Fusion Monster Card and Special Summon that Fusion Monster from your Extra Deck. (This Special Summon is treated as a Fusion Summon.) The Fusion Monster's effects cannot be negated this turn.
Rare