A wise MUD admin will realize that you HAVE to always have some unwinnable situation if you want a healthy playerbase. This should, however, be much more subtle than a #### invincible mob at recall. Ideally it should be more of a sort of nagging in the back of the mind that slowly grows until the players are utterly obsessed.

Blaise Pascal writes about this phenomena in great, excruciating length in his Pensees. A recommended reading for mud admins, for the insight it will shed into human nature. Most libraries will include it- ask them if they carry the "great books of the western world" series, which usually should include Pascal.

This does not by any means need to be mob related. It could be politics, an unsolved puzzle or mystery, or even the existance of a particular actual PC that everyone hates.

Show me a riled up, ****ed off player and I'll show you a player who isn't likely to leave the MUD any time soon. Assuming it is done right, and with subtlety.