The question does not have really clear answer because it depends at which time of development you mean.
The brunt and brute were the only two enemy "types" (meaning that it was pretty much "normal guy" and "big guy" concepts) that always were 100% in the design. Then there was a few other suggestions on stuff like flying enemies, swimming enemies, etc. But as the project change direction a lot of times, many of these become a bit unfitting.
I do think that the latest monster we had in mind, but did not make, was a monster that attacked you with sanity bursts. The concept name was the magician or something similarly cheese and the idea was that an even the shortest encounter would be very bad for the sanity. It was not much more fleshed out then that, and I cannot recall us having any real dicussions of look story, or whatnot other than the basic mechanics. Still, would have been fun to see how the creature would have turned out. Some other time perhaps?