Mewtwo's Counter Picks

Back air while a little hard to get used to at first is arguably one of the best edge guarding tools in the game because it is surprisingly strong and has insane range

Remember that mewtwo has his tail hitbox back from melee. your tail attacks now extend your hitbox considerably, and mewtwo has a harder time reaching the ground. remember to watch that tail!

Down tilt can start most of mewtwos combos, in neutral use lots of shadow ball and tilts!

Don't be afraid to throw out a Disable from time to time, it actually has a fair bit of range and can even be used to out-space some sword-fighters if used properly.

Forward air is actually godlike and can combo at low percents and kill at high percents. You can set up into it at around 60% with down-tilt and maybe up air if you know how to