There are multiple ways that you can do this:
You can use the
orange fire cylinders found through out the maps by pressing
and then throwing them at enemies or spots you want gas to be with
.
Or by using either the
pyro grenades with any class, in match they can be equipped by using
and the corresponding
, then once equipped you can deploy them by pressing
.
Lastly you could use the heavy class with the
flamethrower.
This is by far the easiest way, in my opinionMine seemed to count it as an elimination, even when the screen said assist, whenever I did the most damage to said enemy.