You can send 1 "Gem-Knight" Normal Monster or 1 "Gem-Knight Fusion" from your Deck to the GY; Special Summon this card from your hand in Defense Position. When your opponent activates a card or effect, while you control a "Gem-Knight" Fusion Monster (Quick Effect): You can banish 3 "Gem-Knight" cards from your GY, including this card; negate that effect, then all "Gem-Knight" monsters you currently control gain 1000 ATK. You can only use each effect of "Gem-Knight Hollowcore" once per turn.