There are multiple ways that you can do this:
You can use the
green gas 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
gas grenades or
gas mine gadgets, in match they can be equipped by using
and the corresponding
, then once equipped you can deploy them by pressing
.
Mine seemed to count it as an elimination, even when the screen said assist, whenever I did the most damage to said enemy.