Liberator Eto (SUDA-EN023 Secret)

This card is the English language version
Cannot be Normal Summoned/Set. Must be Special Summoned (from your hand or GY) by paying half your LP, while your opponent has a Monster Card in their field or GY with an effect that activates in the hand or Monster Zone in response to a card or effect activation. You can only Special Summon "Liberator Eto" once per turn this way. This card's Special Summon cannot be negated. This face-up card cannot be used as material for a Fusion, Synchro, Xyz, or Link Summon, also during your turn only, it is unaffected by monster effects activated on your opponent's field.
Attribute: DARK
Secret Rare
Monster
From the Yu-Gi-Oh set Supreme Darkness