[4] The player must explore complex levels, sometimes searching out keys to progress, while engaging enemies in fast-paced combat using a variety of weapons.

[citation needed] Developers Mike Voeller and Jason Mojica met while working together at Raven Software on Singularity.

Around that time, Mojica reconnected with Voeller and decided to leave his job at Starbreeze Studios to join the project.

[4][6] Later, the two recruited Andrew Hulshult for the soundtrack and Josh "Dragonfly" O'Sullivan from the Doom modding community to work on level design.

[8] The launch trailer and later gameplay demos[9] were created with a pre-alpha version of the game showcasing a typical level.