From the back cover:
The new class strikes again!
After awhile, goblins cease to be frightening, gold loses its luster, and underground dungeons, ruined cities and ancient temples cease to be an attraction. Your players want new sights, new adventures, and new threats to challenge their skill, might, and wits.
Fear not! For those Referees who need to give their game that spark of something new, we present MONSTROUS MAYHEM, the first source-book for Spellcraft & Swordplay! Within these pages you will find a new Elite Path, rules for hedge magic and legerdemain, mass combat, underwater adventures, a host of new monsters and more!
Designed for the Deluxe Edition of Spellcraft & Swordplay, but completely compatible with the original or revised editions, MONSTROUS MAYHEM will become an invaluable resource for players and Referees alike!