Scuba Steve
Smash Ace
I do agree that the match-up is difficult, but I think it's important to note the tools that Pikachu has to help him out in the match-up as well as his weaknesses in it. Pikachu's vertical kill ability with upsmash, upsmash -> Thunder, and uptilt -> Thunder allow Pikachu to score much earlier kills on Mewtwo than many other characters who have to deal with killing him off the side because of his very good recovery and buffed weight. Pikachu also has an easier time dealing with Mewtwo's teleport antics and hover antics better than some other characters. Granted, this is probably because I main Ganon and have only started picking up Pikachu as a serious secondary several weeks ago, but dealing with what I guess could be called hover shield pressure is much easier as Pikachu. Here's an example of what I'm talking about. Basically the Mewtwo is hovering behind your shield, usually out of a teleport, to avoid getting grabbed, but during his hover he can also harass your shield with aerials. Ganon doesn't really have any answers to this besides rolling because of his poor OoS options, but Pikachu can use his upair OoS to get a combo started. Pikachu also has an easier time getting back to stage against Mewtwo than most other characters because of his godlike recovery. Edgeguarding is a strong point of Mewtwo's game and having the ability to get around that helps a ton.
TL;DR
Still a hard match-up because of Mewtwo's tail, but Pikachu has a lot of things that can help him out in this match-up
TL;DR
Still a hard match-up because of Mewtwo's tail, but Pikachu has a lot of things that can help him out in this match-up