Gem-Knight Ruby Secret Rare

"Gem-Knight Garnet" + 1 "Gem-Knight" monster Must first be Fusion Summoned with the above Fusion Material Monsters. Once per turn: You can Tribute 1 face-up "Gem" monster; this card gains ATK equal to the Tributed monster's ATK on the field, until the End Phase. If this card attacks a Defense Position monster, inflict piercing Battle Damage to your opponent.