Specialized build designed to be used with grouping setups with Ensnare (or other Helminth abilities, but preferably Ensnare for easier headshots).

Once the enemies are in a group fire a round into the crowd and with Spirex's innate AoE you should proc gas on every enemy in there at least once. With Multishot, you could get up to 4 Gas procs per enemy. Since Gas is a lingering AoE effect, every enemy's proc effectively damages everyone else.

20 enemies in a crowd, each with 4 gas procs = 80 Gas procs on everyone doing damage.
10 Enemies in a crowd, each with maxed gas = 100 Gas procs.

The damage goes higher the more enemies there are. Strip armor to see 200k+ DoTs, sometimes a million depending on the crowd.