Learning to reliably teleport in whatever direction I choose, and judging distance to ground when doing so (to minimise landing lag by finishing on the ground) opened up my Mewtwo play a huge amount. Ledge cancelling teleport expands on that BIG TIME.
Furthermore, Mewtwo's air dodge is godlike, and can offer some really interesting approaches and approach-stuffers. Mix up AD forward into fair, backward-then-forward fair, backward into FCSB release, and SH straight up into fastfall Nair.
Fastfall Fair is awesome. Falling Uair is also awesome.
Confusion is your new god. the second (in one jump) doesn't alter aerial momentum and can surprise/dismay your opponent, particularly if they are a counter/shield-junkie - the best followup to a successful confusion is shield, but if they don't try to Fair you or tech, consider D-Smash.
SH Disable is underrated for stuffing approaches against all but the largest disjoints.