I just posted this in the Mewtwo board but I figure I'd put it here too:
I'm testing out Mewtwo's Jab and it seems to have some interesting mixups with the new shield stun mechanics. Some of the math might be off but I'm testing this in all in training mode.
Mewtwo's base damage for Jab 1 is 4%. This gives it 5 (4?) frames of shield stun.
Mewtwo's rapid jab activates 6 frames after the first hit.
This means that in order to beat his rapid jab after shielding with an attack it needs to come out frame 1. Not even Sheik's frame-2 jab can beat it.
OoS options such as grab can beat it, but these can be out-spaced in a lot of instances such that the OoS move whiffs and rapid jab hits. Probably things like Mario Up B will win, however.
Rolls can get past that the rapid jab, but here's the fun part: Mewtwo if he chooses NOT to rapid jab will recover more quickly than the opponent's roll.
This is something I'm sure a lot of characters can do (haven't test it extensively but based on the frame data of other characters I'd assume so), but this is on top of Mewtwo's other jab properties. Jab 1 has no recoil effect when its disjoint hits other attacks (within 9%), what's sometimes referred to as trample. Jab 1 also combos into grab, and Jab 1 into Disable is also a mixup.
Basically, this means that Mewtwo's Jab is potentially able to win against Attacks, Grabs, AND Shields. Against attacks, possible trample. Against grabs, no grab armor means potentially stuffing the grab attempt. Against shields, a mixup.