Characters In Game: Gil
The following were notes made while this was in development. They do not necessarily represent the final state of the thing.
As seen on [this page], C-Gas is essentially a knockout gas, commonly carried in gas grenades. Klaus' forces carry them, presumably to pacify as necessary. It is very fast-acting, and appears to fill an entire room -- for game purposes, probably within a ten-foot radius, or something like that.
Normally, C-Gas knocks its victims out for about 36 hours. Obviously, if we're going to use it in-game, we either need a weakened version of it, or we need to invent an antidote. Based on [this page], it's pretty clear that no such antidote exists in canon.
There seems to be an even stronger version (v3, p115), apparently called "D-Gas", powerful enough to knock out even Von Pinn.