I entered the coal caves after a reset today, and it was literally the highest spawn I have EVER seen. I'm not sure if a DM had anything to do with it, but - it was really fun, and a bit intense. I've noticed no shadow demons seem to spawn anymore. It goes from fiends, to greater shadows it seems. Also, in the last room, there weren't just shades... there were GREATER SHADES. Woo.
But, I'm curious. That's the highest I've ever seen it, but it's been on the fiends to greater shadows for a while now... yet I've never seen the greater shades form. If a DM didn't do the placing, and that's how the spawn should naturally go, then it never ever ever gets up to the greater shades, and maybe should be upped a bit for that cave. Seeing as how only half the final room was greater shades, that would seem to imply that all the shades would eventually turn to greater shades, which would mean that the spawn was only partially into the ULTIMATE SPAWN OF DOOM (tm) phase.
Also, curious what's different about the greater shades. They seemed to do a bit more damage, but otherwise, I chewed through them easier than the actual shades.