Metagross "Machine gun stomp" do you have to reveal hand?

[deckmaster]

Metagross has an attack that does more damage for each Energy card in your hand. However, its attack, Machine Gun Stomp, does not state anything that allows the owner to reveal his or her hand to show how much damage it can do. That being said, if a player attacks with Metagross's Machine Gun Stomp, would they have to reveal their hand to show how much Energy is there to increase the damage output?

 

[PokePop]

I think you've misread the attack.
It does 10 more damage for each card in your hand.
Not just energy cards. All cards.
So, you can show the number of cards in your hand to the opponent without revealing your hand.
Just fan out your hand and show the card backs.