Saihate no Paladin

[KrayZ33]

I don't know why you fixate yourself on exactly *that* look. This is just an example.

Again, there are tons of horror-*anime*shows that have ugly/scary looking monsters in them that are sometimes pretty disgusting to look at without the whole show looking like the shitty Star-Wars animes that came out recently.
Hell, there has been a harem show recently that is somewhat similar to Slime, that featured a very minor side character for like 2 epsiodes, that was some kind of Lich, and even that one looked way cooler and evil than him.
You are really not using your imagination and knowledge and experience here.

And the "he had to move like that" doesn't really count. It's magic that he moves in the first place, so magic is magic and magic allows him to do whatever the author decides he should be able to do. It's no less or more believable either way.

It's about the intention of what they wanted to show and when I look at the LN pictures (and I didn't read it, so maybe the LN is weird in that regard), it seems like the monsters are supposed to look more grim-dark than how they look in this show.
It's also why the battle with Gus was kinda weird to look at when he was floating there, looking super normal, and MC nearly pissed his pants.