Fought 2 so far, I think they was both the same.
It appeared to be in a jump suit, or maybe a hazmat.. and I think carrying a fireaxe, both times it gave me a chest with 2 ears and 3 fuel.
The first time was during a rush, 2nd time was about 20 seconds after a rush ended, music played and it appeared.. not sure if they're suppose to happen outside of rushes or not.
Lv 29 missions
Balance seemed fine, I deploy in full teams to help with xp balancing with a mix of melee and range (range bias) w/doc
Impossible to tell what it resisted and what it didn't.. took about 30 seconds to kill.
Since I've only fought 2 I can't really recommend any balancing changes yet but I would however request either an extension to mission time (say 30 seconds) when they appear or perhaps a timer freeze as they require your full attention and eat up time.
Edited by Joe Sixpack, 15 June 2016 - 11:51 PM.