A little suggestion.
How about a cyborg zombie? It makes sense in the context of the world, and can be fun to see.
Instead of replicating existing enhancements, they can be made unique in that they cannot be killed unless using something like an explosion or a critical hit. They will self-repair after 20-100 turns and attack again. The effects of butchering them are up to your imagination, Whales It might require computer skills to disable them (reprogram them to aid you at high levels?)
For reference, imagine something like the blood skeletons in mostly any Castlevania game.
I think Whales is trying to balance difficulty and fun with the emphasis on fun. That right there, sir, would not be fun. Not even a little bit.
Why so? It doesn't need to be powerful like a hulk. It can be as powerful as a normal zombie, just with that gimmick, that you can't rest with one of those corpses nearby (EDIT: I guess the Blood Skeleton reference flew by). And even so there are solutions like dragging the corpse out or butchering it somehow.
Did you understand anything more powerful than that?
I am interested in your reply, please elaborate.
When I'm playing a game I'm almost always turned off by the "this enemy can't be killed! Run away or use your special (x) to get rid of it!" gimmick. Enemies are not as difficult or engaging as they are plain annoying. I know it's not exactly the same concept, but it's similar enough. After a few encounters with it I'd only be facepalming when another appeared on screen. I can't see how a wave of zombies would be more entertaining to deal with when one of these were present.
How about a chance of outright destroying it on kill anyway (both with normal kill and always on an overkill (shots that do enough damage to destroy an enemy corpse))
Oh yes, that's what I meant with "criticals", sorry for not being clear...language barrier and stuff. A headshot or a good melee hit should be more than enough to get it down.
As for the progressive thing...well, they would still achieve the same design effect, so that can work too.
If they're only as powerful as a regular zombie and a they can be killed by powerful blows, what would be the point? Most players don't openly engage zombie waves until they have the skill/ammunition to destroy things in 3~ hits/shots (or in the case of shotguns, one shot). I see what you're trying to get at, but I don't think it'd be fun in practice. These zombies would be low priority (or perhaps last priority) and pose very little extra threat, aside from occasionally standing up in a fight and getting knocked away again. It would serve the same purpose as a regular zombie with no added difficulty, wouldn't it?
Yes, but they also serve to surprise you. I know of a bunch of games where enemies respawn after some time, and it's not an exact science, some care is needed depending on genre. However, the main function of the idea is preventing you from ignoring corpses lying around, sort of like a reverse Necrozombie.
If you happen to find a solitary one that enters a safe house while you are boarding it, and don't take care of the corpse, it'll come to bite you unless properly dispatched. That I didn't want them to be powerful is because they might freaking wreck you if they are anywhere like Hulks.
Many players ignore corpses and stuff, while it's natural, we are talking reanimated corpses roaming the streets. One that is able to put him/herself back together would be fairly natural. Also, depending on who you ask, it can be annoying or challenging. Consider a lot of people plays in varying ways, like hoarding, disregarding learning (pure melee) and so on. Are you saying that there is no possible way such an enemy can work?