Yo. I took the texture for the creature. It's called "finale_floor01", and it's in materials/sabiru/finale.
Sabiru is one of the creator's previous projects, and they said they needed an excuse to recycle some assets, so this is probably just an example of that. You can see the texture in some screenshots from Sabiru, too. Along with other assets that are in this map.

Texture: https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3255216173
Sabiru: https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?l=dutch&id=3231114000&searchtext=

It's on the floor and roof in one of the screenshots, hence the name. I don't know what "finale" implies because I haven't played Sabiru yet. Anyway, I don't know what the actual creature looks like, I wasn't able to find it. But I'm pretty sure with this and some of the other screenshots people have taken, you can pretty well piece together what it looks like. Sorry about the yap session.