I tested alot of dp fadc backdash punishes today.
I’ll list all the stuff I’ve found here, it’s not all practical but it’s good to know.
Feel free to test stuff, and tell me if there’s anything I missed.
For the U2 punishes, you have to be aware of the fact that the opponent can hold thier focus and delay the backdash, I feel that U2 should only be used on a hard read or actual reaction to the backdash on the characters that you can use non-reversal U2 to punish.
Also, if you’re buffering U2 and looking for a backdash but they forward dash, you can always punish with throw anyway because it will out prioritize the buffer.
Ryu, Ken, Akuma.
[details=Spoiler]Mk. Ruffian
Mk.Super
Ex.Ruffian
U2 (reversal or non-reversal)
Far st. Roundhouse[/details]
Seth and Dan.
Spoiler
U2 (reversal or non-reversal)
Oni.
[details=Spoiler]Oni’s backdash leaves him quite close to the opponent after his dp fadc, this
makes for some interesting/easy punishes. >:D
You can take a slight step forward and:
Cr.Hk
Far.Mk
Far.Hp
Cr.Hp (Tight window)
Forward Mp (This hit’s meaty so you can actually Connect an u2 or sweep after!)
These punishes also work:
Mk ruffian
Ex ruffian
Mk Super
Far st. Roundhouse
Ex Criminal
U2 (reversal or non-reversal)
[/details]
C.Viper.
[details=Spoiler]Mk Ruffian (Only from point blank)
Mk Super (Only from point blank)
Ex ruffian
U2 (reversal only)[/details]
Sagat.
[details=Spoiler]Mk Ruffian
Mk Super
Ex Ruffian
Lk Ruffian
Lk Super
U2 (non reversal, you HAVE to wait for the grounded frames otherwise it’s going to hit him
out of the air.)
Crack kick > follow up.
Walk forward slightly, cr.lk xx Special move
Walk forward slightly, Cr.roundhouse.[/details]
Cammy, Decapre, Adon and Poison.
Spoiler
… I couldn’t punish any of these at all… 
Evil Ryu.
[details=Spoiler]Mk Ruffian
Mk Super
Ex Ruffian
U2 (reversal or non reversal)[/details]
Guile.
[details=Spoiler]Mk Ruffian
Mk Super
Ex Ruffian
Far st.Roundhouse
U2 (reversal or non reversal)[/details]
Fei Long.
[details=Spoiler]Ex ruffian
Mk ruffian/super (only from point blank it seems)
U2 (reversal or non reversal)
[/details]
Yang.
[details=Spoiler]Ex Ruffian
U2 (strict timing non-reversal, have to wait for the landing frames)[/details]
Now bare in mind that all of these were tested at point blank, Fei and Viper seemed to avoid
some punishes completely when they were a bit further back.
As I said feel free to correct any errors if you find anything new… Happy punishing! 