2018 · ソースブック（プレイを拡張するルール／オプション）
Hideous Creatures
A sourcebook for Trail of Cthulhu campaigns, this book presents a bestiary of Lovecraftian creatures through conflicting accounts, variant abilities, and alternate interpretations. Each entry connects an entity to myths, historical events, and folk tales, while providing physical clues, occult evidence, adventure seeds, and handouts for investigators to uncover. The creatures are presented as mysteries and sources of madness as well as threats to fight or escape.
スキルベース（スキルを購入または獲得）ポイント制（ポイントを割り振ってスキルや能力を得る）ダイス（主にd6）
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。