And the thing is? Until we found Mewtwo was planned, that was a very legitimate stance to take. But once we find out the data, it was false. After Young Link was turned into Toon Link, I could understand that reaction. If you didn't know about the Forbidden 7. But all you have to do is simply look that up and find out "Okay, I was wrong." Also, notably, Mewtwo had little relevance during Brawl's development. He had no notable appearances at all beyond of course being in FireRed/LeafGreen. And small Events here and there. He wasn't in the Anime at all, no movies, no major promotions. He had nothing on Lucario. Now he's back with a vengeance. Or she, if her new movie version means anything. Dang voice actors.
I first thought it was Shadow Ball. But I am quite pleased that Smash 4 isn't overrun by 1st Gen Pokemon again, having at least 2 from other Gens, so it was just plain awesome.
For the record, I preferred transformations, but from a gameplay standpoint, they kind of sucked in practice.