Niv-Mizzet, Supreme is a rare Legendary Creature — Dragon Avatar card from March of the Machine: The Aftermath (MAT), collector number 140.
Flying, hexproof from monocolored Each instant and sorcery card in your graveyard that's exactly two colors has jump-start. (You may cast that card from your graveyard by discarding a card in addition to paying its other costs. Then exile it.)