The Invasion is a 1997 partial conversion for The Ultimate Doom which replaces all four episodes. It was created by Paul Fleschute (Moe) and it includes a wide variety of changes, including new enemies through DeHackEd, many new textures and sprites, new music, and a new storyline which pits the player against the Aldorian alien race as they attack several Starbases owned by the USEC. Through its many custom graphics and enemies, the WAD manages to create a peculiar atmosphere that still remains unique to this day. A sequel, Invasion II, was released the following year.
The WAD could be considered somewhat notorious for containing numerous thing placement bugs, situating monsters, weapons, ammo, barrels, typeless things and other objects outside the playable area on many maps (and also occasionally typeless things inside). The misplaced monsters make achieving 100% kills impossible on E1M9, E2M2, E2M4, E2M8, E3M8, E4M2, E4M3, and E4M5, as well as 100% items impossible on E3M9.
Monsters and other changes
This WAD features four built-in demos. All require Ultimate Doom v1.9 to view them. The demo levels are: