I beg to differ. Mewtwo isn't "bad" in the sense that he can't put up a fight against the rest of the cast, and he definitely isn't the worst character in the game. Not even close. Now, the thing about Mewtwo being bad is that, in any game, a character is only bad relative to the rest of the cast. In Mewtwo's case, he's not your usual low-tier character. Mewtwo is average in a game where most characters are above-average, and, thus, he comes off as subpar. I've said this before, but Mewtwo is like Bill Nye in a room full of Isaac Newtons. He's totally fine on his own, but compared to his competition, he pales a little bit.
As for Mewtwo being the worst character in the game, that's simply not accurate. Mewtwo is fast, powerful, has a top-notch punish game, possesses a variety of tools, and has a very lengthy, variable recovery. He definitely has some strong suits that keep him out of the bottom-tier. Also, Mewtwo does have quite a few combos, so racking up damage isn't as big a problem for him as some people seem to think.
Furthermore, I disagree about Mewtwo being unable to put up a fight against most of the cast. As a long as a character isn't overly fast, such as Sonic or Captain Falcon, Mewtwo can probably break even with them. Mewtwo is fast enough to keep away from most characters, Shadow Ball allows him to out-zone a majority of the cast, and his top-of-the-line punish game complements his defensive playstyle nicely. Plus, tools like Confusion give Mewtwo a way to cancel out some kinds of approaches, which complements his punish game. Essentially, with a few exceptions, as long as his opponent isn't too fast, Mewtwo probably has a fair chance against them.
Now, what's the problem with that? Most characters in the game have more advantageous match-ups than Mewtwo, which makes them objectively better characters. So, as a result of "above-average" being the norm, average characters like Mewtwo are left behind. It's all relative, you know?
I mean, I'm not saying that Mewtwo is some secret top-tier character, but he's nowhere near the worst character in the game. He has tools that keep him out of the bottom-tier, and he can break even against most of the cast. At this point, I would say that Mewtwo is somewhere in the low-tier. He's not bottom-tier, though, and he's certainly not the worst character in the game.
In regards to buffs, I do think that they would be very nice, but I also agree with @
Rhus
's statement about us Mewtwo mains needing to learn to work with what we've got. We're already discovering some pretty cool things, such as N-Air true combos, and if we keep working at it, I think Mewtwo will probably move up a little bit on the tier list. Ultimately, however, I think that a combination of hard work on our end and buffs from the devs' end is what's necessary to make Mewtwo a viable, tournament-worthy character.