Dampen Thought is a common Instant — Arcane card from Modern Masters (MMA), collector number 39. Current market price: $0.13 (foil $0.38), TCGplayer market prices via Scryfall.
Target player mills four cards. Splice onto Arcane {1}{U} (As you cast an Arcane spell, you may reveal this card from your hand and pay its splice cost. If you do, add this card's effects to that spell.)