Mechanics

moves you can’t buffer are stance moves
negan does not have a stance you enter by doing qcf
meanwhile, paul’s deathfist is actually crouchdash 2
and you do crouchdash with paul by doing qcf
same with yoshi and kazuya
yoshi’s dp2 is bufferable because the move is just dp2, not [stance you enter with dp] 2
meanwhile, with kazuya, dp enters his crouchdash

[more detailed link wanted here]

Toe Kick (“Recovery Kick” in practice mode; performed w/ d+4 while FUFT) has varying advantage on block depending on the character that performs it.

Lee

High crushes up until the first active frame, where he just starts evading highs, and getting hit during and after this frame counts as a float.

Law

High crushes up until after the first active frame, otherwise, same as Lee’s. This means a trade with his slide is not a float, but gets full CH properties.

Shaheen

The same as Lee’s, except his float frames start almost right away. This means the only time you get full CH properties is hitting him in the first (couple of) frame(s) of his startup. His also recovers into FUFT the fastest, making electric punishment on block much more difficult. It also doesn’t low crush at all.

Lei

Almost the same as Shaheen’s, except he is in float the whole time, from the stance until he recovers after the move. His high crushing is kept throughout his stance and the startup of the move, up until the first active frame (meaning electric will trade with his slide, but cannot hit him before that frame)