Contra Doom aims to replicate the gameplay of Contra, particularly Contra III: The Alien Wars, including the ability to hold two weapons at a time, one hit deaths, and scoring points. While Contra III is best represented here, some elements from other games are taken, such as Super Contra (Arcade), Contra: Hard Corps, and Contra 4.
The Ultimate Doom, Doom II, TNT: Evilution, Plutonia Experiment, and Heretic IWADS are currently supported.
Weapons are obtained by picking up eagle shaped tokens with a letter on them. You can hold two weapons at a time. Picking up a weapon you already have equipped will upgrade it.
Spoiler: Description of weapons
Death & respawning
Unlike normal Doom, you can freely respawn when you are killed, as long as Contra Doom is loaded last. However, you will lose whatever weapon you had selected at the time and lose your Rapid Fire upgrades.
In Single Player, you have a limited number of lives, starting at three. If you lose them all, then the Game Over screen will appear. You can earn an extra life upon reaching 20000 points, and then every 60000 points after that. After a Game Over, you can restart the current map you're on from the beginning, but it'll be a fresh start; no weapons, no score, and only one bomb. In Cooperative mode, or if the Infinite Lives CVAR is enabled, you will simply receive a score penalty instead that scales depending on your difficulty level.
The game will try and respawn you where you died, but sometimes you'll respawn back at the level's start (although the level won't reset). This occurs when you've been telefragged, suicided with the "kill" console command, or your respawn point is obstructed by something (best seen with crushing ceilings).
In Heretic, the Wings of Wrath lasts until the end of the level, just like in Hexen. You'll respawn with them if you die after picking one up.
Compatibility with map packs
Contra Doom works with most Doom or Doom II map packs, but Contra Doom should be loaded last or you may not be able to respawn in single player. However, any DeHackEd modifications, particularly monster replacements, may not function properly. See below for a .zip file containing patches that allows proper support with certain map packs. When playing with TNT: Evilution and Plutonia, it is recommended that you load their retrospective patch included with Contra Doom so that you get the proper automap names and text screens. When playing with Heretic, load its retrospective patch so that you get the correct player sprites, palette translations, automap names, and text screens.
Contra Doom also includes an optional music wad that replaces the in game music with select songs from Contra III: The Alien Wars and Contra: Hard Corps. It works with both Doom II and Ultimate Doom. For Heretic, you'll get a variety of tracks taken from the Castlevania series, mostly from Super Castlevania IV, Dracula X, and Bloodlines.
Spoiler: Included patches
Contra Doom specific CVARS
(If the ZDoom version doesn't load, try getting a recent SVN version of ZDoom of GZDoom. Also, load it after any PWADS you might add or you may not be able to respawn in singleplayer)
(Zandronum users: You must use the 3.0 alpha to load Contra Doom)