The demon Mara. What can we say about a giant penis demon who throws around Double Entendres like Halloween candy and in some games is a woman? To boot, one of his/her typical weaknesses is ice.
Any time an enemy uses an attack on a party member who is immune to that attack, twice. Moreso if it's a game with the Press Turn system, in which blocked attacks carry a one-turn penalty and drained and repelled attacks result in a loss of all turns.