Disco Inferno Disco Inferno
Have 10 enemies burning simultaneously. Unlocks the "Graug" mask, "Coal" material and "Fireborn" pattern.
Stick a Fork in Me, I'm Done Stick a Fork in Me, I'm Done
Set an enemy on fire and kill him with the "Motherforker" melee weapon. Unlocks "The Gas Mask" mask, "Candlelight" material and "Flammable" pattern.
Not Invited Not Invited
Kill 10 enemies within 10 seconds using the Piglet Grenade Launcher. Unlocks the "Firefighter's Helmet" mask, "Burn" material and "Flamer" pattern.
Set a Bulldozer on fire for at least 10 seconds. Unlocks "The Chef" mask, "Toast" material and "Hot Flames" pattern.

The following appeared on March 25, 2015 and were replaced on March 26, 2015.

Achievement locked Nothing
Achievement locked Like the
Achievement locked Smell of
Achievement locked Napalm.