Okay, if you look in the custom mob spawner download, there is a word document explaining that the options don't work right if you run mocreatures without the mob spawner installed too. You have to delete the existing config file and reinstall both together for it to work. Type /cms in game to get to a horribly configured options menu. It's really just awful since they took the GUI out.
I call this No' Creatures now. Worlds are spawning with no animals at all in them. Tried MSC2 but can't get the GUI to open, so I'm stuck. Really don't feel like changing a bunch of config files by hand, especially if it won't get anything to spawn anyway. Not sure where to go from here.