No, you came in here to explain to us how our character works, insinuating none of us know how to play him correctly yet. Then you go ahead and say that maybe we are right and it's just that Mario has a bad matchup against Mewtwo. You literally left no room for the fact that you just lost to a bad char. It's either "he's not that bad" or "he's good against Mario". It couldn't just be that you got outplayed I guess.
As I said Mewtwo is huge combo food for mostly all of the zonebreakers/rushdown characters, Mario being one of them.
I don't believe Mewtwo to be the worse char in the game, and I think he still has a lot of untapped potential and strategies, but I do believe he's undoubtedly low tier.
Mewtwo's biggest weakness, at least in my own opinion, is that he struggles against offensive play. All of his hardest matches (again in my opinion) are offensive combo-oriented chars like Sheik, ZSS, Mario, Falcon, Fox, etc. He has some other problems in certain MUs like not being able to hit Pikachu and Kirby, but that's not really what we're discussig here.
Basically by the little context you have given me it seems like you were trying to zone out Mewtwo and bait him, like you would another of the offensive approach chars. B-Air wall his approaches, etc. This matchup doesn't work like that, Mewtwo shines when there's a spacing battle since he can space so well. Mewtwo sucks when being attacked full-on having no options to dodge them, no attack to counter them and no mobility to DI them, plus being so big that everything hits him.