Gem-Knight Ruby (BLMM-EN136) - Battles of Legend: Monster Mayhem 1st Edition

"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.