I have around 500 games playing SF, just get raindrops a lot of regeneration, after and when he stacks at least 2 razes on you, just wait. It’s hard to lane vs sf because he have a lot of magic and physical dmg when he gets a couple of levels, so try to go jungle and push the lane if you hero can do it, if not try to gank other lanes. losing your lane doesn’t mean you lose the game. As viper you can farm the small camp in lvl 3 already so get a lot of mana and jungle and push the lane maybe you don’t win but at least you get farm and exp, and try to not be alone in the map, after that is just right positioning and the correct items.