How about Stoker being able to pass the gas-filled corridors with less health damage than other mercs.
This could make him a sneaky basterd of the game in Terminal and even in Underground (he could go down several seconds before the the 1st obj explodes)
Would rather see a new merc with like a Gas based ability (think something like tear gas grenade) that would have that as an secondary ability. Like a special filter for his gas mask that allows him to walk unharmed through gas for X amount of time. Cooldown for the filter to charge electrons or something 
If I remember correctly his gas mask was only ‘cosmetic’, one of the eye lenses was missing, any gas could get in the mask.
…which puts forward the impression that he is either mentally unstable or disfigured …or both.
But going back to Glottis suggestion, yes, it fits with that character.
They could alternately have it as one of Stoker’s loadout augments
