FCandChill: Nice observations. Those are quick fixes. I don't mind the animation being different (the head wobble), but on the masked man it is indeed strange because his neck bounces up and down and the head doesn't. I'll make his head move up and down too.
Da_GPer: I think I might review the concept.
protomank: I never thought of them that way, specially because the big one looks like he's dead instead of wearing a skull mask and they both seem to be wearing long sleeves.
At least now I have reorganized the tiles in the rom (reassigning tiles was like hell) so making conceptual changes is easier. Here's old and new tiles:

In my opinion making them clearly cannibals is an interesting concept. I never knew what they were supposed to be, but maybe that + their lack of animation (life) made them so uneasy and disturbing to look at. That uneasiness is lacking in the new sprites. I'll wait and see if there's more feedback about this here and then come back to these.
Just a reminder: their in-game behavior is a lot zombie-like, except for the occasional projectile shooting. I can already adjust their move speed, their shot speed, and how often they shoot.
edit: the US manual mentions them as cavemen, while the japanese one seems to say they are simply underground people (confirmation needed. If anyone has the japanese manual please share. I couldn't find it anywhere on the internet).
edit2: There is one unused enemy in the rom that gave me a real scare when I tested it. I think I'll add it somewhere with original graphics.