Heretic Eradicator

When your opponent would Special Summon exactly 1 monster, while this card is in your hand and your opponent has 4 or more monsters that cannot be Normal Summoned/Set in their face-up field, GY, and/or banishment (Quick Effect): You can negate the Summon, and if you do, destroy that monster, and if you do that, Special Summon this card (while you control no monsters, this effect and its activation cannot be negated). You can send this card from the field to the GY; halve the ATK of 1 monster on the field. You can only use each effect of "Heretic Eradicator" once per turn.