i was told (by someone running a local event no less) that in order to fully use sharpedo ex's darkness blast (where it does 80 damage and you get to discard an energy off the defending pokemon) that one must discard an actual darkness energy, that dark-metal or any other kind of card providing dark energy could not be substituted. this struck me as preposterous. for example i see players discard DRE to use raichu d's metallic thunder all the time. what on earth is the difference between the wording of raichu d's attack and sharpedo ex's???