I always noticed that the Robo Zombie counted as a zombie hero, because I would get XP for vanquishing a zombie hero. I was sort of surprised by this as hero characters are normally playable, however the Robo Zombie is not. I do not find these enemies appear that often, sometimes in story quests or Ops, but generally I find them somewhat annoying, but thankfully not too annoying. Their high health and knockback at close range can make them quite tough to defeat. I would not have to face against multiple of these enemies at the same time. Changes that I would suggest include making them being able to be eaten by Chomper (as sort of a counter to these enemies, although at the same time I do not know if this seems feasible), remove the knockback at close range, and to reduce the damage at long range so they are slightly less annoying at range, although to increase the damage further at close range to make them more of a threat.
The Sasquatch Imp only appears in the Sasquatch Boss Hunt (as you mentioned already) and while I find them quite annoying to defeat as they are small, fast and like to appear in large numbers, they are not as annoying as the Yeti Imps, as they do not freeze you, although the fire damage can deal a lot of extra damage and negate your regeneration for a while. That being said, their threat scale can be made redundant by getting up to a high place where they cannot reach or get up to you. Overall though, I like seeing variants of enemies such as the Sasquatch Imp (fire variant of Exploding Imp) and would not mind seeing them appear more often in the future, even as summonables. Changes I would suggest include reducing their explosion damage but reducing the delay before they explode as well.
