RTF is a global modification that replaces all towns in the game.

If I'm not mistaken, didn't you once have incubi and some other demons?

Only incubi, as far as I remember. It was a replacement for elementals, like a demon summoning spell. There were standard demonesses, cerberuses, and probably simple demons with the incubi. I remember that the game would crash with hell horses, so I sadly put someone random in there.