Unstable Amulet is a uncommon Artifact card from Modern Horizons 3 (MH3), collector number 421. Current market price: $0.33 (foil $0.32), TCGplayer market prices via Scryfall.
When this artifact enters, you get {E}{E} (two energy counters). Whenever you cast a spell from anywhere other than your hand, this artifact deals 1 damage to each opponent. {T}, Pay {E}{E}: Exile the top card of your library. You may play it until you exile another card with this artifact.