Farewell to Arms is a common Enchantment card from Unhinged (UNH), collector number 56. Current market price: $0.24, TCGplayer market prices via Scryfall.
As this enchantment enters, choose a hand attached to an opponent's arm. When the chosen hand isn't behind its owner's back, sacrifice this enchantment. If you do, that player discards their hand . . . of cards. (The lawyers wouldn't let us do it the other way.)