Heatran-GX UNM 25

Once during your turn (before your attack), if this Pokémon was on the Bench and became your Active Pokémon this turn, you may move any number of Energy attached to your Pokémon to this Pokémon.

This attack does 50 damage times the amount of Energy attached to this Pokémon. (You can't use more than 1 GX attack in a game.)