Here is my "2000 Matches with Mewtwo Celebration Post". It's basically a list of reasons why I don't think he's good, and I'm hugely disappointed in him. He seriously just needs significant changes to be a good character. His major issues (besides lots of hitbox issues):
1) Light as a feather - I am fine with this, but it is definitely a problem. Jigglypuff has the best aerial control in the game for playing it safe, and Rosalina has a living wall in front of her. Nothing justifies Mewtwo's weight. Even his teleport, which one might think could get him out of sticky situations, maintains a hitbox during its time of travel - he isn't just reappearing, he's traveling, and you can smack him down during it.
2) Defensive, but no actual good defensive options (Bowser has Fortress, Mewtwo has...?). Nair needs to have a huge startup hitbox behind and below him, or it needs to have zero landing lag and less startup (currently 11 frames to jump + start the move, compared with Mario or Sheik whom both get their OoS Nair at 7 frames IIRC).
3) No way to pressure opponents offensively. His aerials are too floaty, and his only good ground attack is dtilt. The only way to fix this is to give him better approach options, and to make anything reflected by Confuse immune to reflection. Otherwise he'll still have a huge set of unplayable matchups like Fox and Falco. Sakurai should really add crouch-canceling into the game, because Mewtwo with crouch cancels might actually have offensive options that don't require short hops into fast-falling to position his only good move better (dtilt, as you all know).
4) No response to offensive rolling. One of a few characters in the game with this problem. Nair buffing fixes this as well. Alternatively, Sakurai should
give his Shadow Ball charging hitbox back. You know, the defining feature that Lucario stole and got to keep for some reason.
5) No good options after jumping, and no good ledge get-up options. Let's say Mewtwo goes for the Fair...then what? Nothing, that's what. It produces so little shieldstun that it isn't safe to use - you have to burn your double jump to "run away" after trying. An opponent can run in and punish. You can double jump into a second Fair, but it can be shield grabbed (lol) between hits because of where you have to stay. You can use Confusion for more aerial spacing to land better, but Confusion isn't safe on its own. Basically, Fair can't be used as a poke like Ness' can, because Ness' Fair multi-hits to make the move safe for spacing. The move should hit a lot lower than it does, and create more pushback.
6) Shadow Ball, his defining move, is mediocre. Garbage, even, compared to Samus' charge shot. As a small harassment tool, it is beaten out by numerous other options. It needs to have faster startup, at least.
7) Confusion is slow as hell. You can't reflect anything on reaction. It has to be predictive because of the massive startup: 12 frames. Compare this to Fox's Reflector, which starts on frame 6. 6. That's half the startup. Mewtwo doesn't have 12 frames to reflect fast projectiles on reaction - he just gets hit. Furthermore, most other reflectors in this game are better than Confusion, and if you're using Confusion, it's probably to keep yourself from dying from your own Shadow Ball getting reflected back at you by a superior reflector.
8) Project M teleport. Just sayin'. If Mewtwo is going to be light as a feather, he should have some godlike stuff to make it worthwhile. If you compare Mewtwo's moveset to other characters, he has weaker tools than most mid-weight characters. There's just nothing "fantastic" or interesting about him to justify his weight. Rather than make him heavier, I wish they would justify his weight class by giving him something that terrifies other players. When they first revealed Mewtwo, I was ecstatic because I thought they gave him his Project M teleport. Then I found out it was his air dodge. ***. If you don't know what the Project M teleport is like, check this video out:
https://www.youtube.com/watch?v=yMd6wAoqsJ4
Fail, Sakurai. Mewtwo has the worst teleport in the game. The float would be badass, too, but we can't have fun things.
9) How about some combos/damage? Yeah, he has some badass combos at low %, and he can get you to ~40% in no time off of a dtilt. But...then what? His only combo past the low % is jab to dtilt, and it isn't even guaranteed against sex kickers like Luigi. Plenty of other characters have great combo setups, but Mewtwo loses all of his aside from Nair shenanigans, which involve guessing which side the opponent will land on (LOL - why is this random?), and he can utilt into Usmash against some characters in some standing stances at point blank range - amazing, right? The biggest problem with Mewtwo is that his damage is crud. Each tail flick does ~5% damage like he's Sheik, but he has to work
so much harder for those hits than Sheik does. You could double his damage on everything, and then it
might be reasonable.
10) I want 10, so I'm going to think of one more...oh yeah, his dodges. Why were these nerfed? Mewtwo has one of the worst side dodges in the game. Again, this is part of the discontinuity with his weight class. Why make it so hard to survive with this guy? Why not make him do a teleport dodge, like Palutena (or, you know, like Mewtwo when he air dodges)? Why not make his air dodge hold him still instead of making him continue downward? Hell, give him the only directional air dodge in the game. Anything to make him stand out and justify his weight class.
I think it says something when one of the most awaited DLC characters of all time has resulted in almost no one playing him. To be frank, I was disappointed on release day just because the teleport was so uninteresting - in my fondest dreams, I was going to be able to act out of it. Instead I got a slow, limited, light, and light-hitting character. It felt good to say all that.