Wid0maker
[10] Knight
I did some testing on this, and as far as I can tell, the best option to punish aB at tip range is JS 6A. That's only if both hits of the aB are blocked. If you only block the B, JS 6A will whiff. You can also punish with CE. 3K works too but only if you're a little closer.To be honest I don't know what to do about aB spam, for me it is one of the stupidest attacks in the game. If you have any tips feel free to share.
EDIT:
found some other punishes for Cervy's aB at close range:
JS/GS 3B
JS 4A (kind of surprised that this is able to punish, but it does..though you have to be close range when you block)
JS/GS 3K
JS 66AA (need to be quick)
CE