Phobos: Anomaly Reborn

Phobos: Anomaly Reborn is a PWAD level set by Christopher Lutz released in 2003. The episode features a similar design as Lutz's other levels, with highly detailed and realistic environments. Examples of such include a moving train and a hangar with ships and transport rails. The episode was included in Doomworld's Top 100 WADs of All Time list.

Thematically the episode serves as a replacement of the first Doom episode. However, it is much more difficult than the original, with bigger puzzles and stronger enemies appearing earlier. For example, the baron of hell appears in the second level instead of first appearing as the episode's boss.

Levels

 * E1M1: Hangar B
 * E1M2: Toxin Refinery
 * E1M3: Dissolution
 * E1M4: Railbender
 * E1M5: The Dig Site
 * E1M6: Subterra
 * E1M7: The Beneath
 * E1M8: Anomaly Reborn
 * E1M9: Lost Barracks

The zip archive on idgames archive includes a walkthrough.