Deathmatch is a multiplayer game style pioneered by Doom in which players face off against each other, their computers connected to a common server via a network.
- A point, called a frag, is granted to a player whenever he or she kills an opponent.
- Frags are deducted when a player commits suicide, or dies in a crusher or damaging floor.
- Upon death, players restart at a random deathmatch start.
- Players spawn with all keys, and keys are never placed on the map (there is currently no clean way to circumvent this).
- When the level ends, the intermission screen gives each player's frag count. (Note that many PWADs specialized for deathmatch play do not contain exits.)
Cooperative gameplay, often referred to as co-op or coop, is a multiplayer game mode in which human players cooperate against a given game's monsters. Cooperative play is the default game mode if deathmatch mode is not explicitly specified at the command line.
Because the players are not adversaries under coop rules, they are visible on one another's automaps, and each can even "look through the eyes" of his companions (perhaps inspired by Electronic Arts' 1993 tactical game Space Hulk), though their status bars cannot be viewed.
Vanilla Doom has support for up to four players in multiplayer games. The players are made distinct from each other by altering the suit color of each player. Player 1's suit is green, player 2's is indigo, player 3's brown and player 4's red. Many source ports increase the number of players supported and several ports also support custom player skins and skin colors.
Differences from single player mode
In vanilla Doom, certain game interface features behave differently in multiplayer mode. For example, any player can pause or unpause the game at any time, and using the "save" command causes the game to be saved in the same slot on each machine. Also, when accessing the in-game menus (options, sound, save, load, etc) the game does not pause.
During the design of a map, objects can be flagged to appear only in multiplayer games. In stock maps, this is normally used to insert extra weapons and powerups, which provide a more balanced supply of armaments in cooperative play and more interesting "arms races" during deathmatch play. Beginning with Doom II, most stock levels also contain extra monsters, usually boss monsters; these provide more fearsome opposition for cooperative play and act as booby traps in deathmatch play. (Because of the extra monsters, some speedrunners enjoy the challenge of completing max runs in multiplayer mode, using DOS utility programs to create a fake "second player" who neither moves nor attacks.) Some level designers use the multiplayer flag to block off shortcuts introduced for singleplayer compatibility, like the torches in Memento Mori's maps 14, 15 and 29.
Chocolate Doom is a source port which attempts to mimic almost all of vanilla Doom's original behaviour. This port remains compatible with Doom, but not on a network level, since TCP/IP and IPX are incompatible.
ZDoom-based source ports
ZDoom uses a TCP/IP architecture for all network play; the game state is tracked on a peer-to-peer system. Players in search of co-op allies or deathmatch opponents can use Doom Connector or Player Connector to set up a game. This system also works with LANs, but an Internet connection is also required.
Four further ports have improved on ZDoom's networking code by incorporating client/server network architecture:
- csDoom, based on ZDoom version 1.22, was the first client/server multiplayer port. Now deprecated by Odamex.
- Odamex is derived from csDoom 0.62 (with a new maintainer), its aim is to retain oldschool compatibility with vanilla Doom, yet providing a client/server style of multiplay.
- Skulltag features new weapons, customizable AI "bots", entirely new variants of multiplayer rules, and sample levels designed around ZDoom's non-vanilla features.
- ZDaemon is derived from csDoom by its ex-developer NightFang. Originally using csDoom's ZDoom 1.22 version, it has since updated to ZDoom version 1.23 beta 33.
These ports are capable of running large-scale multiplayer games more smoothly, as they were written specifically with network play in mind. For multi-port use, Internet Doom Explorer is recommended to see all of the servers.