Ok, so my son and I were testing out a deck for him. We're still new to the game, so please bear with me. He had a Skamory eX in play and had 3 metal energies attached to it. The metal energy has a special ability that causes damage to be reduced by 10. Does this ability stack with each metal energy card attached to a pokemon? So he had -30 damage to each attack. Is this correct? Thanks!