Is there any OS for him? Or it completely absent?
General option selects like wall splat/throw tech OS exist for him, so at the very least he has those. He probably has others to use on offense. @MnTLetalis might know of some.
What is it tech? Any links?
I know couple of his OS like: Shadow Ruin/Instinct and other shadow/instinct. But, what is other one?
As far as I know he cant OS his normals to catch backdash like other characters can. He can OS jump ins to catch backdash like everyone else, and there are some specific sorta usefull OSs to beat crossup mixups. For example you input shadow ruin and hold it so if they cross up you get shadow natural disaster. Works sometimes against spinal and fulgore. Other than that I dont think he has much
upflick can os tall characters, whether they jump or not your get the flick,l you can combo shadow recapture if either hits, or ruin through wall if you dont have recapture. you can ruin without wall, but thats not always safe…
corner l rock into st.h into l rock knocks fulgure out of wake up dp, kim out of reversal and everyones backdash, evertones dp actually, all shadow counters, and if they jump you can do flick into shadow recapture or cH into shadow recapture.
only people who can really get out of it are omen and mira and spinal (sort of). even the best gargos out there can do almost nothing against this