I only ever played this matchup from the Falco perspective before the Mewtwo nerfs, so I don't know how much of this applies but here goes:
The most important thing you want to learn is powershielding lasers. Laser approaches are literally the only way Falco has to open you up, if you deny that from him it's a very easy matchup. You don't have to powershield every single laser, just practice and get the timing down so you can
threaten his obvious approach attempts with powershields. That alone will give you a huge edge.
As Mewtwo you will want to control center stage as much as possible and wall out Falco with well spaced tilts and bairs. Abuse utilt/fair/uair juggles, pivot grabs, dtilts into grabs, teleport nairs (I don't know if this is still a thing), etc. Falco has a hard time getting in on your huge range and safe pressure, stuff him out of whatever he's trying to do. Also remember that lasers barely do any damage, don't panic if Falco starts projectile camping you, just be smart and patient. The pressure should be on him to approach you, don't let him get in. Convert on your grabs, it's incredibly easy to edgeguard Falco as Mewtwo. If you get a grab near the edges of the stage, bthrow or fthrow puts Falco in a terrible position. You should also aim to finish your combos with anything that throws him offstage. Use shadow ball to hit him out of his recovery if he tries to sideB directly into the stage, all other options are easily covered by grabbing ledge/drop down bairs or fsmash. A Falco off stage should be a dead Falco, don't drop edgeguards.
In short: Powershield lasers, abuse your range, look for gimps, don't drop edgeguards.
Here's a video of an old money match I found, it's pre-nerf mewtwo but the matchup should be played pretty much the same.
