Imprint — When Thought Prison enters, you may have target player reveal their hand. If you do, choose a nonland card from it and exile that card.
Whenever a player casts a spell that shares a color or mana value with the exiled card, Thought Prison deals 2 damage to that player.
The second ability triggers only once per spell. If the spell shares both a color and a mana value with the imprinted card, Thought Prison deals 2 damage, not 4.