These tests are not perfect (and done in training mode)! I don't have the tools to test this frame by frame, so they are probably not 100 % correct, but they should come pretty close.
Momentum cancelling if you're hit horizontally:
MK is on left side of FD (roll to edge).
Diddy to the right of him (roll into MK on the edge to get near enough).
MK does dsmash
No DI; Diddy won't die off the top, but to the (right) side.
180 %
survives with airdodge->smashsideB
survives with airdodge->jump->sideB
survives with bair->smashsideB
survives with bair->jump->smashsideB
181 %
survives with airdodge->smashsideB (survives without the need to hold left)
survives with airdodge->jump->sideB (survives without the need to hold left)
survives with bair->smashsideB (survives without the need to hold left)
survives with bair->jump->smashsideB (survives without the need to hold left)
182 %
survives with airdodge->smashsideB (survives without the need to hold left)
survives with airdodge->jump->sideB (survives without the need to hold left)
survives with bair->smashsideB (after/during sideB you need hold left, else you won't survive)
survives with bair->jump->smashsideB (survives without the need to hold left)
183 %
survives with airdodge->smashsideB (after/during sideB you need hold left, else you won't survive)
survives with airdodge->jump->sideB (after/during sideB you need hold left, else you won't survive)
184 %
won't survive
Other stuff:
With no momentumcancel Diddy would die at 154 %.
The doublejump does help a bit against horizontal momentum:
161 % - survives with airdodge->hold left [won't survive at 162 %]
171 % - survives with airdodge->doublejump (+hold left) [won't survive at 172 %]
Momentum cancelling if you're hit up:
Falco does an upsmash; no DI
119 % - won't survive without momentum cancel (at 118 % Diddy survives)
125 % - can survive with nair (fastfalled, of course)
126 % - survives with any fastfalled aerial (except nair?)
DI to the direction Falco faces
129 % - survives (with fastfalled aerial, maybe not nair)
DI behind Falco
136 % - survives (with fastfalled aerial, maybe not nair)
(seems like dair really doesn't change much (you activate your fastfall 1 frame faster with dair))
If you're DIing to one of the top corners momentum cancelling get's a bit more tricky.
Last time I tested it was a long time ago so I'm not too sure anymore how it was...
but I think that this was the best method...:
bair (fastfalled)->wait a little bit (so you won't die off the top because of a little momentumboost from sideB/doublejump)->(smash)sideB
EDIT: alright, I searched for my old testings and found the post:
But I noticed something... if you get hit into a top corner and bair +fastfall then double jump I died immediately after using the DJ, but when I waited a little bit before using the DJ I survived (without the double jump and only a dair or bair+fastfall I died). I also survived using fair(&fastfall) and then DJ, you just have a wait a little bit before double jumping... the thing with dair is, it has so much ending lag that if you DJ after it immediately you'll survive.
And you only die from bair+DJ, because you DJ too early.
I could also survive with airdodge+fastfall and dj, but I also had to wait a little bit before DJing or else I died. (this testing was done at 160 % (middle of FD, MK did dsmash on Diddy (training mode)); I ALWAYS held up on the controlstick while getting hit)
At a bit later % (165)... you can't survive with airdodge then fastfall and DJ. No matter what I did I always died.
I could survive with dair+dj and bair+fastfall+wait a bit + dj and with bair+fastfall+sideB.
At 171 % I couldn't survive with dair because it has too much ending lag. But I could survive with bair+fastfall+waitjustalittlebit+sideB (DJ KOd me). It was also possible to survive with fair+fastfall+DJ+sideB...
172 % I could also survive with bair+fastfall+waitjustalittlebit+sideB, fair had too much ending lag.
