Mid-tier.
He's a strong, slow character, who flies far and dies quickly (He's the second lightest character, after Jigglypuff, in fact).
Despite this flawed combination, Mewtwo is a really good in defense options.

First, his specials.
Shadow Ball: Main spacing tool. Takes a while to charge up but does having gimping/edgeguarding potential imo.

Teleport: A great recovery once you get used to it. Can also be used to reliably dodge attacks after enough practice.

Confusion: This is a huge asset against projectile based characters. It can temporarily stun the opponent, being a great combo starter. Also, this is a very good projectile reflector, as even almost a second after I used the move, it still reflected the attack. You can kinda also combo into this from a jab.

Disable: Garbage. At least from what I've seen of it. The trick to it is you need to have eye contact with the opponent, making it particularly hard to pull off against pretty much anything. The only good thing I can see here is you could get lucky and catch an opponent in this off of a Confusion, and you can combo it from a jab, if you're lucky, but that's about it.

Throws:
DThrow: Meh... It doesn't really combo into anything, I just use it a lot because I'm used to DThrowing with Ness.

BThrow: Probably his best throw. Can reliably kill at the edge of the stage at just past 100% typically does around 10% too.

FThrow: It looks cool and typically does 10%. Low knockback.

UThrow: About as strong as BThrow. Can be good for mindgames and K.O.s.

Aerials:

Fair: Definitely his best aerial. Low ending lag, high knockback, decent range.

Bair: Good range, good combo potential, that's all.

Dair: Nice meteor smash. Haven't explored it much apart from that.

Uair: same as Bair.

Smash Attacks:

Down Smash: Pretty good for edgeguarding. Sadly, it only attacks in the front.

Side Smash: Great knockback, great range, great damage output.

Up Smash: Hard to hit most of the time on the ground but catching an opponent in the air, and their damage is around 80% or up is dead.

Other:

-Down Tilt and Up Tilt are good combo starters.
-Shadow Ball doesn't hit unless you shoot it anymore.
-He has a really quick roll.

Probably more to be added.

Not a bad character at all.
Good review.

DThrow: Meh... It doesn't really combo into anything, I just use it a lot because I'm used to DThrowing with Ness.

n-air at low percents, f-air at mid percents

You forgot his Nair. It's good for reading rolls or just as a way to accumulate damage.

lol mEwtwo is that rare character that I like to play as but suck donkey dick with

and ur rite his fthrow is great especially in multi man