I was trying to remember the one with crabs. (Insert your own Kirk and Space Babe of the Week joke here.) What an unfortunate choice of transmogrifications.There are three that are coming rigth to my mind:
The Laertian Gamble
Most likely the upmost ridiculous plot I've ever seen, combined with a more than poor writing style, a complete catastrophy.
Windows on a lost World
Chekov, the cannibalistic giant-crab, does I need to say any more?
Chainmail
The most of the Gateways-series was not really entertaining, but this one was a pain to read. Boring characters, a plot close to nonexistence and overall large amounts of boredom.