Repost from Vergil General thread:
Vergil’s stand S is normally -13, but is -7 after being push blocked.
Vergil’s Upper Slash (H after S) is normally -8, but is -2 after being push blocked.
If you do S-H and the opponent push blocks at S, your H will whiff and you will be at -7 frames total.
If you do S-H-S and the opponent push blocks at H, your S will whiff and you will be at -17 frames total.
The above calculations for whiff are assuming you are just repeatedly chaining Upper Slash without delay. If you delay an input to catch your opponent’s push block and they happen to push block right before your next attack comes out, you will be at a greater disadvantage (-14 or -24, respectively). In other words, if your opponent can perfectly time their push block with your input, they can potentially make the string more punishable, though this is practically impossible. If you’re just mashing the string, pushing at the H is prudent. Pushing the S will make it somewhere between difficult and impossible to punish the string.
Advancing Guard is not a cure all for getting around this string. The H can still be canceled into specials on block and it sports nice block stun. It’s also 5 frames to start, so it’s possible to frame trap between S and H. Delaying the cancel and messing with the timing can get you some nice results. I don’t think it’s a strategy that is overpowered or one that you should abuse, but it can be put to use.