Castle Greyhawk

From the back cover:

Deep beneath the keep of Castle Greyhawk, a really nasty device is creating all these gross, mutated, and unpleasant monsters that are running wild throughout the castle. The call has gone out for heroic, fearless, and kinda foolish adventurers to out-hack, out-slash and sometimes even out-think hordes of doughmen, headless mice, manic bee queens, really bad dead things, burgermen, crazed chefs and movie moguls. If they survive these and much odder obstacles, the characters still have to find the nasty monster creator and put it out of business.