Gem-Knight Ruby (DT05-EN034) - Duel Terminal Ultra Parallel Rare

Gem-Knight Garnet + 1 "Gem-Knight" monster // Must first be Fusion Summoned using the above cards as Fusion Material Monsters. Once per turn: You can Tribute 1 face-up "Gem" monster you control; this card gains ATK equal to the Tributed monster's ATK, until the End Phase. During battle between this attacking card and a Defense Position monster, inflict piercing Battle Damage to your opponent.