Is it a word? What about oppositorial?

Don't you mean adversarial? I've never heard adversial, but adverse is another adjective. Same goes with the other word. The adjective is oppositional.

Thank you for the clarification.

I don't find any mention of it in the B&M OED and there's no mention of it in onelook. It gets about 8800 google hits but some of them are really for adversarial. There does seem to be some legitimate presence but it may be a mistaken spelling of adversarial. If so, it's a relatively popular one.