Four Against the Abyss: A Supplement for Four Against Darkness

From BoardGameGeek:

When standard dungeons do not pose much of a challenge anymore, your experienced heroes may want to go deeper, looking for greater rewards. Once all of your characters reach 5th level, you will want to start using this book! This is an expansion to Four Against Darkness designed for character levels 5 to 9. It includes; using a d8 for combat and saves new monster reactions new, more powerful monsters expert skills that your characters can learn new spells for wizards and elves rules for madness, disease, vampirism and lycanthropy details of hirelings and professionals your party can hire plots for campaigns updates to all charts, including new monsters, encounters, special events, and treasure Take your party into the Abyss and step into the tier of experienced adventurers!