She’s one of the characters that can freely dance around the stage (Seth is another), so Fei has a tough time keeping her in check. If you knock her down in the corner, that’s one thing, but Viper standing up is a whole 'nother story. No matter what you do though, the match-up is going to be a pain in the ass if the Viper you’re playing just keeps moving and stays off the ground/out of your range.
Somethings that really help me in the matchup:
- Reversal her cr.MK and cr.MP’s with CW.
–You’ll catch her TK before it starts unless she uses the HK version, which is suicide and won’t happen. If she tries to cancel into EX Seismo, you also interrupt that by way of not being in range of the blow, and by outlasting her I-frames with your active frames.
- cr.MP at max range on her wake-up if you can’t get a safe jump.
–If she EX Seismo’s, you can block before it hits. If she HK TK’s, you won’t get knocked out since the knuckle needs to be relatively close to hit low (I’m quite sure, but please re-test this. It’s worked for me a few times already). If she simply blocks, you get your +2 on her and can use that for offense.
- Focus nearly all Burning Kicks. Dash cancel for safety.
–If she hits this high, you can get a crumple easily. If she hits this low, you can backdash/forward dash safely since none of her moves are fast enough to catch that. If it whiffs, you’ll have SOME chance to escape before she lands and grabs you, whereas Ultra would leave you wide open for lv3 Focus.
- Safe jump her if you can get the distance right.
–Due to her slow moves, it’s easy to do this, although you really can’t follow up with much since the varying invincibility on her moves make it tough to choose which one to pull next. A late Flame Kick would work, but you have to be good with timing it.
- Walk for most of the match.
–Jumping leaves you open to Burning Kicks, anti-airs, and surprise Seismo’s. Remember that she can combo into her Ultra from nearly a full-screen away. Sometimes she’ll go through 2-4 Seismos and cancels to chip you, but you can just eat the chip. If you manage to close the distance, focus on getting LP Rekka x1 perfectly. You can sometimes get away with Rekka x2 since her normals are slow, but don’t risk it unless you delay the second.
- Don’t jump if you’re next to her and stay out of the corner.
–Anti-air HK TK will let her juggle right into an Ultra, even on trade. Air Burning Kick will let her juggle into an Ultra too.
Reference battles: K Mada, PlayinCODNaked. PlayinCODNaked is a beast with Viper, can’t consistently beat him. Learning a lot from those fights though.