When you take damage from your opponent's card effect or their monster's attack: Apply the appropriate effect based on the type of damage.
• Battle: Special Summon 1 monster from your GY, with ATK less than or equal to the damage, and if you do, end the Battle Phase after the Damage Step.
• Effect: Inflict double the damage you took to your opponent.
You can only activate 1 "Split Mirror of the Underworld" per turn.