Is there a good tourney-legal card that would work great in an all Water deck that would allow energy to be moved freely between all the active & benched pokemon?
Mewtwo d (ds) - one time only but as much as you want.
Gardevoir d (ds) - one energy at at time every turn per one you have.
Energy Switch - one energy once ... not a great choice.
Sure you can. DS is legal for the next 3 months. After that, yeah, it's gone ... but the OP never said anything about next format. He asked for stuff that was legal with the implication being now.
