Gonti's Aether Heart is a mythic Legendary Artifact card from Aether Revolt Promos (PAER), collector number 152s. Current market price: — (foil $12.49), TCGplayer market prices via Scryfall.
Whenever Gonti's Aether Heart or another artifact you control enters, you get {E}{E} (two energy counters). Pay eight {E}, Exile Gonti's Aether Heart: Take an extra turn after this one.