Bark of Dark Ruler (LOD-010) - Legacy of Darkness 1st Edition

You can only activate this card during the Damage Step of the Battle Phase that a Fiend-Type monster on your side of the field attacks or is attacked. Pay Life Points (in multiples of 100 points) to decrease 1 of your opponent's monster's ATK and DEF by the same amount of points until the End Phase of that turn.