The situation is I have a Mew EX with the ability versatile in the active position. I have a Zoroark on the bench with Foul Play.
I use Mew EX versatile ability to use Zoroark's 2 colorless attack Foul Play to use my opponent's Mega Charizard EX's Crimson Dive for 300 damage. His Mega Charizard EX is on my opponents bench. I do so by spending only 2 colorless instead of Charizard's 5 energy. This is because Zoroark has no stipulation on having the same energy required (he only needs 2 colorless to use any attack.)
Have I made a legal play?
I use Mew EX versatile ability to use Zoroark's 2 colorless attack Foul Play to use my opponent's Mega Charizard EX's Crimson Dive for 300 damage. His Mega Charizard EX is on my opponents bench. I do so by spending only 2 colorless instead of Charizard's 5 energy. This is because Zoroark has no stipulation on having the same energy required (he only needs 2 colorless to use any attack.)
Have I made a legal play?

