Ghostfire Slice

Four damage at instant speed for a single red mana is a rate that historically demanded a land sacrifice, and this card gets there by taxing a deckbuilding choice rather than a card cost. The reduction fires only when an opponent controls a multicolored permanent: not two mono-colored permanents on the same board, but a single gold card, hybrid spell, or split-cost bomb resolved onto the battlefield. Most cost reducers reward you for what you are doing; this one prices its own efficiency to the opponent's manabase, and against a mono-colored board it simply stays a three-mana burn spell. That conditional is the balancing lever, and it is aimed with unusual precision. Devoid makes the spell colorless while keeping the in the cost, which cuts two ways: it ducks color-based protection and feeds effects that want colorless cards, but you still need red to cast it, so it never becomes a universal splash. The instant timing carries the rest. Four damage clears most of what an early creature curve produces, and holding it up threatens a burned-down planeswalker or lethal reach to the face without ever tapping out on your own turn. As asymmetric hate it is sharper than the raw number suggests, because the discount rewards reading the field correctly (punishing an opponent who committed to gold cards) rather than committing your own list to a shape.