Gonti's Aether Heart is a mythic Legendary Artifact card from Modern Horizons 3 Commander (M3C), collector number 294. Current market price: $0.71, 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.