Dampen Thought is a uncommon Instant — Arcane card from Champions of Kamigawa (CHK), collector number 57. Current market price: $0.21 (foil $0.40), 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.)