Deathloop is a 2021 first-person shooter immersive sim video game developed by Arkane Lyon and published by Bethesda Softworks.

Arkane implemented asymmetrical multiplayer, an unused gameplay mechanic from its unreleased game The Crossing that enables a second player to control Julianna and hunt Colt.

[1] Deathloop has a multiplayer mode in which the player can alternatively play as Julianna, a Visionary tasked with protecting the time loop and killing Colt.

Juliana has a unique ability named Masquerade that allows her to swap her appearance with any non-playable character (NPC) in the game, enabling her to blend in with crowds and stay concealed.

[11] Alternatively, players can use stealth tactics to silently evade their opponents, distract them by throwing bottles, or kill them with traps or suppressed firearms without being detected.

It is now owned by the AEON Program, which the scientist Egor Serling founded to use the island's unique properties to gain immortality by living in an infinite time loop.

Serling attracted eight other eccentric, talented individuals to his cause, the Visionaries, and scores of fanatical followers called Eternalists dedicated to serving them.

He learns he was a member of Operation Horizon, the original military expedition to Blackreef decades earlier, but was accidentally sent into the future by an experiment that went awry.

Arkane previously experimented with the roguelike genre with Prey: Mooncrash (2018), and Deathloop was built to further expand on the idea of remixing gameplay using a limited amount of assets.

[23] Colt's powers were designed to be similar to those in Dishonored to maintain a level of familiarity to fans of Arkane's past works.

[27] Familiarity with each location enabled players to master their gameplay skills and understand the game's myriad of systems earlier.

[28] As levels were designed to be replayed, the level-design team worked to ensure each route toward an objective had their own advantages and drawbacks.

Unlike Dishonored, which had a morality system to judge the player's actions, Deathloop maintained a neutral stance throughout to avoid facilitating a specific playstyle.

[22] The developers removed quick-save functionality from the Dishonored series because they wanted players to see the consequences of their actions and react to them, being spontaneous rather than loading a saved game to bypass failures.

[30] Bakaba described Deathloop as a "murder puzzle" and an "inverted Cluedo" in which players must achieve the "Golden Loop" by eliminating all Visionaries within a single day.

[33] Unlike immersive sims with a minimalistic head-up display (HUD), Deathloop's user interface readily provided players with information.

[31] The developers wanted fighting Julianna to be a challenge and ensured Colt had a slight advantage over her through the "Reprise" ability, which allowed him to respawn twice.

Besides time-travel and time-loop films like Groundhog Day, Edge of Tomorrow (2014) and the Back to the Future trilogy, the game was also influenced by the French comedy La Colle (2017) and The Fourth Dimension (2012).

[40] To create a surrealistic atmosphere and depict a world frozen in time, the team contrasted the 1960s aesthetics with military structures that were common in the 1930s and 1940s.

Fristad Rock focuses on the contrast between an old, derelict bunker and an elegant, lavish casino; and Karl's Bay serves as the major party and entertainment location in the game.

[49] The visual direction was also inspired by the styles of the Swinging Sixties and the contemporary depiction of the era as seen through Guy Ritchie's The Man from U.N.C.L.E.

The developers were inspired by 1950s and 1960s science-fiction and horror films and television shows, such as Not of This Earth (1957) and My Favorite Martian (1999), as well as A Clockwork Orange (1971) and The Thing (1951).

Salta also worked to ensure his score reinforces the time-loop theme; some chord progressions repeat in a variety of ways depending on the player's actions and location.

[59] The game's development was completed on 5 August 2021; Arkane confirmed it had been declared gold, indicating it was being prepared for duplication and release.

[64][65] Deathloop was released for Xbox Series X/S on 20 September 2022, alongside a "Goldenloop" update that introduces a new weapon, a new ability, new enemy types, cross-platform play and an extended ending.

[72] Writing for GameSpot, Tamoor Hussain said "observation and dynamic thinking" are as important as combat in Deathloop, and players are rewarded for carefully planning and understanding the system and rules established in the game.

[75] Purslow also said the non-linear investigative gameplay is satisfying, and remarked players will constantly make "thrilling discoveries" as they recognize the causal relationship between their actions and in-game results.

He added Blackreef is a "theme-park dystopia" that paints a "glorious picture of a ruinous, elitist society and spectacle", compared with Dishonored's grim atmosphere.

[85] Some critics liked the way conventional world-building tools such as in-game computer terminal chat logs and audio flies provide key information for players to progress.

[73] Hussein also liked the game's writing and noted the two characters share a complicated relationship, and he praised the voice actors Kelly and Akagha for their performances.