Please help with this basic rule (Help a dad/son relationship)

[SpeedyThunders]

Hello!
My name is Alberto and me and my son Agustin have a little dispute about a basic rule:
I was using a Greninja Breakpoint deck and I had a Greninja card with a grass energy attached to it as my active Pokemon. When my turn arrived I wanted to put an water energy to this card but my son says it is not legal, as it already have the water energy card attached to it and he says this Pokemon can only do the Shadow Stitching attack. His reasoning is that you can't attach more energy cards that it needs, only in the case that a Pokemon has the attack that says the more energy cards it has attached the more damage it can do. He says this particular card only needs one energy card to do the attacks. My reasoning is that the rule says that, when your turn, you can attach one energy card to any of your Pokemon, any, even this Greninja card. I say this Greninja can have the two energy cards, the grass and the water one and he says it can only have the grass one since it was the first I attached to it and that that is that.
Please help us, we enjoy very much this game and we want to keep enjoying this, many thanks!!!
Alberto and Agustín

 

[donavannj]

Hello!
My name is Alberto and me and my son Agustin have a little dispute about a basic rule:
I was using a Greninja Breakpoint deck and I had a Greninja card with a grass energy attached to it as my active Pokemon. When my turn arrived I wanted to put an water energy to this card but my son says it is not legal, as it already have the water energy card attached to it and he says this Pokemon can only do the Shadow Stitching attack. His reasoning is that you can't attach more energy cards that it needs, only in the case that a Pokemon has the attack that says the more energy cards it has attached the more damage it can do. He says this particular card only needs one energy card to do the attacks. My reasoning is that the rule says that, when your turn, you can attach one energy card to any of your Pokemon, any, even this Greninja card. I say this Greninja can have the two energy cards, the grass and the water one and he says it can only have the grass one since it was the first I attached to it and that that is that.
Please help us, we enjoy very much this game and we want to keep enjoying this, many thanks!!!
Alberto and Agustín

You can attach as many energy as you want to any Pokemon. You could even have 10 energy on Greninja if you wanted.

 

[Hands]

yeah, the decks should have come with little rulebooks iirc that should also reinforce what Don said, there's also an online compendium at pokemon.com that has a bunch of super useful answers to more obscure/complex ruling questions which is a very valuable resource