Soul Drain Dragon (SHSP-EN013) [Shadow Specters]

Cannot be Normal Summoned/Set. Must be Special Summoned by your Dragon-Type Xyz Monster's effect, and cannot be Special Summoned by other ways. When this card is Special Summoned while your Life Points are lower than your opponent's: This card gains ATK equal to the difference, but your opponent takes no battle damage this turn. This card cannot attack your opponent directly.