I agree that the killer design is cool. I also like that from my understanding of the background lore (current, dunno if they ever really change them much) it was all sort of accidental. The girl in the story is researching the creature but also stumbled on information about the Entity since it's the same town Mikaela (who the new alt girl goth gf coomerbait survivor is a friend of) and she got abducted by the fog. So I guess looking into both invited them to pursue Olivia and the Entity snatched it up since they both were coming after Olivia and maybe the monster was a better prize. The Unknown is also some sort of information hazard that is based on various ideas to explain disappearances (government mutant weapon, cryptid, serial killer) so it reflects this with the ax, strange shape, and weird hallucigen grenades. Initially I didn't like the design too much but after seeing the lore and the idea it can look like anything will make the skin department cool.
I've always enjoyed the lore but the actual gameplay part of the killer seems like a rehash of ideas and I saw a video recommended basically echoing this. It has an "infection" mechanic and a teleport tacked on for no real reason. So it's like a ranged Nemesis and a hag that can't as cleanly decide where to put its traps (I think if you hold the grenade out it stops the timer). The perks are fine though I like the idea of a speed boost on vaulting as well as a somewhat more reliable Trail of Torment undetectable from kicking a gen.