Kuriboh - Multiply! (GMR)

Card text

When your opponent activates a monster effect, or an opponent's monster declares an attack (Quick Effect): You can Special Summon this card from your hand. You can only use this effect of "Kuriboh - Multiply!" once per turn. Once per turn, when your opponent activates a monster effect on the field, or during damage calculation when an opponent's monster attacks (Quick Effect): You can add to your hand or Special Summon, from your Deck or GY, 1 "Dark Magician" or 1 monster with 300 ATK/200 DEF, then you can change that opponent's monster's ATK to 0.