One More Level released first-person soulslike Valor Mortis recently and discussed how playtest feedback shaped the final game in an interview. Early playtests showed the Eternal Guardsman boss was too challenging and lacked clear signposting that it was optional, causing player frustration. The studio toned down the enemy, made its attacks more readable, and improved level readability. After these changes, the Eternal Guardsman became a favorite encounter for many players.

First-person combat presents distinct challenges for judging attack ranges and tracking enemies outside the camera's view. One More Level prioritized clear attack animations with readable wind-ups from the player's perspective and kept enemies at appropriate distances to stay framed in the field of view. The studio made post-launch adjustments to enemy hitboxes to better match attack animations, preventing attacks from hitting when they visibly miss. For attacks from outside the field of view, the studio added audio cues and an on-screen danger indicator after discovering audio alone was insufficient.

Coming from Ghostrunner, One More Level integrated parkour differently in Valor Mortis. Movement abilities now anchor exploration rather than moment-to-moment combat. Climbable ledges, grappling points, and wall-running let players approach encounters from different angles and add tactical layers.

The studio used Metroidvania-inspired level design with secrets, alternative paths, and shortcuts. All exploration elements remain optional for players seeking more content. The death loop connects mechanically to the narrative through Lucjan Skawiński, a mysterious lamplighter who provides safe havens and respawn points.

World-building relied on historical research of the Napoleonic era, with a "two-step rule" guiding design. Each supernatural element had to trace back to historical truth within two logical steps, with the second step involving the influence of Nephtoglobin, the game's supernatural catalyst. In this alternate history, the Battle of Waterloo became Napoleon's greatest victory rather than his downfall.

Valor Mortis features six weapons supported by Transmutations and individual upgrade trees. One More Level stated the arsenal produces "distinct playstyles" and the studio is monitoring balance, already addressing exploits through patches. The game launched with a single difficulty setting.