Double Impact

Double Impact is a episode replacement PWAD for The Ultimate Doom by Matt Cibulas (RottKing) and Ralph Vickers (Ralphis). It is a winner of 2011's 18th Annual Cacowards, requires a limit-removing port to play. In its original PWAD form, it replaces all nine levels of Episode 1. On 11 November 2013, it has been included with Freedoom: Phase 1, as part of the fourth chapter of the game.

On 13th February 2020, Double Impact was the first community-made mod to be adopted by Bethesda as one of the official add-ons for the Doom Classic Unity port. This version is slightly different. First, the intermission image, which incorporates the cover art from the unlicensed Hungarian novel Doom - Tisztítótűz, was recreated using instead the Eisen character from (specifically, the Eisen skin variant featuring a cap and an eyepatch). Another difference involves the alteration of the d_e1m8 theme to remove references to the theme of Doom 64's main menu.

Freedoom line-up

 * C4M1: Maintenance Area
 * C4M2: Research Complex
 * C4M3: Central Computing
 * C4M4: Hydroponic Facility
 * C4M5: Engineering Station
 * C4M6: Command Center
 * C4M7: Waste Treatment
 * C4M8: Launch Bay
 * C4M9: Operations

PWAD line-up

 * E1M1: Maintenance Area
 * E1M2: Central Computing
 * E1M3: Research Complex
 * E1M4: Hydroponic Facility
 * E1M5: Engineering Station
 * E1M6: Command Center
 * E1M7: Waste Treatment
 * E1M8: Launch Bay
 * E1M9: Operations

Soundtrack

 * E1M1: Untitled track
 * E1M2: Untitled mash-up of "Dark Halls", "Suspense", and "Demons from Adrian's Pen"
 * E1M3: "Sinister" by Bobby Prince
 * E1M4: "Suspense" by Bobby Prince
 * E1M5: "The Imp's Song" by Bobby Prince
 * E1M6: no replacement
 * E1M7: no replacement
 * E1M8: Untitled mash-up of "Sign of Evil" and the Doom 64 Main Menu's theme
 * E1M9: "Demons from Adrian's Pen" by Bobby Prince
 * Victory screen: Untitled track

The Freedoom versions of the levels are edited versions to keep them under vanilla limits, for these ones which exceed static limits. M2 and M3 are swapped to facilitate the secret exit as well.