All new classes are carefully designed to match the power levels of the classic Basic/Expert game.
Rules for poisons. (Essential for assassin characters!)
Advanced options: Optional rules to add extra depth to character creation, combat, and spell casting.
Note that this book is not a complete game! It is a rules module that adds extra player options on top of Old-School Essentials Classic Fantasy: Genre Rules (contained in the Black Box and the Rules Tome). Spell lists for bard, druid, gnome, illusionist, and ranger characters are found in Old-School Essentials Advanced Fantasy: Druid and Illusionist Spells.
The content in this book is 100% compatible with the classic Basic/Expert rules (B/X) and can thus be used with any B/X-based game.