Maybe add a chemist class that uses toxic, caustic, and reactive chemicals and hasses to fight. He can throw vials of acid to damage enemies or use gaseous toxins from a grenade. His non-chemical wrapons would be very weak and his supplies have a very long cooldown but because they damage so much it balances out.
So pretty much his job is blocking enemy movement?
Interesting idea, the gas I mean, me and Alph might not add anymore classes until later on, for now its the current 8.
So guys, sentry gun? (Heck it looks futuristic and is actually a sentry and a mounted gun)

It's called the XM312 btw.