If Mewtwo has a lagless Bair on landing (simliar to Fox's Bair), do any of you think it would be possible for him to create a Wall of Pain?
I don't think so, it already has start up lag and some end lag in the air. Even if landing cancelled all end lag the start up might make it too slow for that. And even if it doesn't then you could only chain a total of 2 together, landing B-Air into rising B-Air, after that the end lag in the air would halt you from continuing.
While I am a massive Mewtwo fan, that is inaccurate.
Pit has fought against gods
Palutena is a Goddess
Super Sonic
Kirdy - Yes, he's ridiculous
Shulk - Don't want to spoil too much in case you haven't played Xenoblade
You mentioned Ganondorf and Link
Samus is a massive threat with all her available upgrades
And then there's meme Captain Falcon
Pit isn't really that strong though and he gets his powers from Palutena.
Link is also severely overrated. Sure he can beat Ganon but that's basically all he would do, most people would defeat him easily.
Samus and Kirby might have awesome upgrades but in reality they are nowhere near as strong as Mewtwo or Ganondorf are, not even remotely.
I don't know anything about Shulk or Ness to be honest.
Super Sonic is too fast and too strong for most of the cast but he is outclassed by a few, he would still be among the strongest because of this.
Palutena is a Goddess, yes, but I feel like even in her own game canon she isn't THAT strong. I could be wrong about her but it seems like her powers are that of Mewtwo, only much weaker.
Ganondorf is immune to anything that isn't holy so probably only Link, Zelda, Pit and Palutena would be able to hurt him, hypothetically speaking. They would probably all defeat him but Ganon would defeat mostly everyone else.
Mewtwo can mind control, brain wash, teleport mountains, destroy buildings with mere thoughts, create tornados, turn back time. This is all without taking into account that he can just explode someone's mind or levitate and constraint them infinitely, or, you know, just teleport them to space. He would definitely be top 3 if not the winner of an all fighter tournament.