2023 · ソースブック（プレイを拡張するルール／オプション）
Between Two Worlds
A third-party monster manual for use with Old-School Essentials and other old-school fantasy role-playing games. It presents creatures and encounters involving interdimensional travel, reality-warping experiments, alien visitors, supernatural guardians, and beings from distant worlds. The collection includes complete monster entries, including a destructive many-limbed angel, a creature made from dozens of people, insect-faced bugbears, slug-like tourists, a frost giant with a dungeon, a world-crossing beast of burden, a ghost-summoning helmet, and an interdimensional spirit trader.
属性／ステータス制（STR、CON、PERなど）レベル制（XPを獲得してレベルアップ）クラス制（パイロット、ウィザード、サイエンティストなど）
ゲーム情報（人数、プレイ時間、対象年齢、クレジット）の出典：BoardGameGeek。