Developed by Wraith Corporation and published by WizardWorks Software, Perdition's Gate is a full 32-level scenario for Doom II released in 1996. Perditon's Gate falls into the category of unofficial expansion, meaning that it utilized the Doom Engine and various assets of the Doom series of games without the express permission of their original creators, id Software. According to Tom Mustaine, one of the game's primary designers, Perdition's Gate was originally envisioned by himself and Bob Mustaine as a third episode for Final Doom which would accompany TNT: Evilution and Plutonia. However, after it became clear that this would not come to pass, the project would eventually evolve into a standalone commercial project with WizardWorks as a publisher. With the objective of getting the expansion to store shelves in an expeditious manner, several members of Wraith Corporation, a collection of Doom mapmakers who were working on a similar WAD project called Hell to Pay, were brought on to assist in development. Though it did not introduce any new gameplay innovations, Perdition's Gate is one of the few Doom level sets to attempt a manner of in-game storytelling, with the intermission between maps providing a few brief sentences to convey a sense of the player's progress through the UAC facility and beyond.
Many thousands of years ago, a war was fought between two alien races, one advanced in the ways of technology and intellect, known as overseers, and the other a savage, violent and barbaric clan. The peaceful overseers attempted in vain to reason with their demonic aggressors, but before long they would be overrun, and as a final countermeasure against the ravenous hordes that beset them, they disabled their inter-dimensional portals, hoping at least to spare other civilizations from their own fate. A few of the creatures were able to access the teleporters before their shutdown, and it was through this that humanity had its first encountered with the monsters. With the portals shutting behind them, the few savage aliens who made it through were quickly defeated by man, but the memories of this battle left an indelible imprint on the human psyche, with many persistent legends of man's struggle against the "demons" being born from it.
Thousands of years later, the incident on Phobos unexpectedly reactivated the portals on the demon planet, allowing the slavering hordes to overrun Mars in short order. Against all odds, however, a single human marine defeated the onslaught and saved Earth from a second invasion. Four years have passed since the second defeat of the interlopers, and the UAC has chosen to renew its research into teleportation technology despite the obvious risks. As a newly minted recruit in the UAC strike force, the player arrives at UAC headquarters for his first day of service to find that all is not well within the facility...
The gameplay structure of Perdition's Gate is essentially identical to that of Doom II, with the same armaments and enemies on display. The player progresses through a linear series of levels (with two optional secret levels), gradually accumulating better weapons with which to fight the increasingly deadly assortment of zombies and demons they will encounter. The goal in each level is simply to reach the designated exit point without dying, preferably killing all opposition along the way. As in previous Doom games, levels hide various secrets areas for observant player to find, which are usually worth seeking out for the beneficial items and power-ups they harbor. In addition, most levels also utilize some combination of red, blue, and yellow keys in order to direct the player's progress along certain paths. Perdition's Gate's main area of differentiation from other level packs is in its difficulty. Purporting to be much more challenging than your average WAD, the game goes as far as to recommend that players start at a lower difficulty setting than they are normally used to. Those who go in expecting an experience on par with that of id's releases may indeed be surprised by the level of opposition they encounter, as even earlier levels will frequently throw droves of monsters at the player.
Tom Mustaine maintains a section dedicated to Perdition's Gate at his personal website, Mustaine.com. The site includes, among other things, the game's original plot synopsis, detailed descriptions of many of the game's levels, and even pictures of concept sketches that were used as references when building maps. It also includes a link to download Perdition's Gate in its entirety, though players must still own a copy of Doom II in order to play.