Something that catched my eye.

[Streetboat]

Big fat monsters could be contextual, like the water monster. It would obviously only work in huge areas. That way, small hallways could be a safe haven(at least, from the big monster. Grunts could obviously still be lurking in the small hallways), as the doorway would be too small for the big monster. It would make a certain area (like the Choir) into an arena, where you have to dart between safe havens to avoid the monsters. When you're in the arena, however, you're completely at the mercy of the big monster. If it were faster than the other monsters, that would be ideal. I can imagine it getting a pretty big head of steam.

But this is all just wishful thinking.