S Kill has been my most annoying match up in the game except Shoals as Jefailey. Shoals is already like 9-1, S Kill vs Jefailey feels pretty bad too. With other characters though I do much better against him. I am actually really surprised that 2 out of 3 of the top players on Steam are S Kill. I am still not sure where I would rate him.
My strategy against him has been to approach him to a spot where I can punish his dive kick on reaction. This forces him to use back teleport until he is cornered. I barely press anything up close except to bait out something. Once he's cornered he has limited options because he can't use his dive kick to escape its too slow and in the corner even his teleports are punishable. Dive/Kick are ideal for this, Kung Pao really good too and Redacted/Sensei not too bad. The biggest problem against good S Kill is that parry, he can cancel his ground teleport into it and can turn a bad situation into a potential head shot. This makes you approach him differently, I aim for his heels which is done best with Dive/Kick and Kung
Pao much less so with Sensei and Redacted.
The other problem with S Kill is that Trick of his (air special). Good players basically use that move for a free kill, IMO its one of the best specials in the game. This makes playing full screen defensive against him a bad option, you always want to be in his grill so he doesn't build safe meter. Once he has that ability though I start staying away and being hyper mobile. I don't know how exactly it homes in but you make it whiff. Most S Kill players like to do it after their 2nd teleport, which is easier to read but those who do it before ensure a kill normally. The cost on it is high so if he misses that's a big win for you.
S Kill is still a hard to read character and that makes him a good online killer. It takes a while to learn his patterns and mix ups. I had to play S Kill for a bit to understand his limitations.