Gas Mask allows the player to survive the effects of a Gas Grenade. This can be beneficial if the player throws a Gas Grenade into a room in order to clear it out, or if an enemy does the same thing. It can also be used when capturing or defending an objective, covering it in toxic gas then wiping out any resistance. If a player has Gas Maks they can survive enemy Chemical Strikes.
Gas Kills: Kill 20 enemies poisoned by a Gas Grenade.
Flashbang, Stun Kills: Kill 20 enemies either flashed or stunned.
Flashed or Stunned Kill: Kill one enemy while either flashed or stunned.
The Amatuer version reduces the effect of flash and stun grenades, limiting them to only one second. It also makes the player's own flashed and stuns more powerful, giving the enemy damage when hit.
Chemical Strikes: Call in 10 Chemical Strike killstreaks.
Gas Kills: Kill 40 enemies poisoned by a Gas Grenade.
Special Kill: Kill an enemy with 2 flash or stun grenades.
The Pro version makes the player's chemical strike and gas grenades change color to purple. The chemical strike lasts 30 seconds instead of the usual 10 seconds. The chemicals and gas will also kill a player in 5 seconds, instead of 7.