A total conversion is a mod of an existing game that replaces virtually all of the artistic assets in the original game, and sometimes core aspects of gameplay. Total conversions can result in a completely different genre from the original.
Examples of famous total conversions include Counter-Strike (1999), whose developers were hired by Valve Software to turn it into a commercial product, Defense of the Ancients (2003), which was the first MOBA to have sponsored tournaments, and Garry's Mod (2004), for which fans created thousands of game modes over its decade-long development.
Many popular total conversions are later turned into standalone games, replacing any remaining original assets to allow for commercial sale without copyright infringement. Some of these mods are even approved for sale despite using the IP of the original game, such as Black Mesa.
An overhaul mod significantly changes an entire game's graphics and gameplay, usually with the intent to improve on the original, but not going as far as a complete remake. This can also include adding revised dialog and music.
Examples of overhaul mods include Deus Ex: Revision, which was given permission from publisher Square Enix to release on Steam alongside the original game, and GTA 5 Redux, which not only improves the original game's textures, but also adds a new weather system, visual effects, and adjusts the wanted system, weapons, and vehicle handling.
An add-on or addon is a typically small mod which adds to the original content of a specific game. In most cases, an add-on will add one particular element to a game, such as a new weapon in a shooting game, A new Unit or Map in a strategy game, a new vehicle or track in a racing game, items in a game like Minecraft, or additional contents in simulation games (such as new pilotable airplanes (e.g., the Airbus A330 or Boeing 787 Dreamliner) and scenery packs for Microsoft Flight Simulator X). This can be accomplished without changing any of the original game's existing content. Many games are flexible and allow this, however that is not always the case. Some add-ons occasionally have to replace in-game content, due to the nature of a peculiar game engine. It may be the case, for example, that in a game which does not give a player the option to choose their character, modders wishing to add another player model will simply have to overwrite the old one. A famous example of this type of mod can be found for the Grand Theft Auto series wherein modders may use downloadable tools to replace content (such as models) in the game's directory. The Left 4 Dead series can also be modded with individual add-ons which are stored in a .VPK format, so that a player may choose to activate a given mod or not.
An unofficial patch can be a mod of an existing game that fixes bugs not fixed by an official patch or that unlocks content present in the released game's files but is inaccessible in official gameplay. Such patches are usually created by members of the game's fan base when the original developer is unwilling or unable to supply the functionality officially. Jazz Jackrabbit 2 has an unofficial patch which adds and fixes many of its features. One downside of this type of mod is that leaked content can be revealed. An example is the Hot Coffee mod for Grand Theft Auto: San Andreas, which unlocks a sexually explicit minigame. The ESRB changed the rating of GTA:SA from Mature (M) to Adults Only (AO). In the fourth quarter of 2005, Rockstar released a "clean" version of the game with the "Hot Coffee" scenes removed (Grand Theft Auto: San Andreas 1.01), allowing the rating of the game to be reverted to its original Mature rating. In May 2006, a similar event occurred with Elder Scrolls IV: Oblivion.
An art mod is a mod that is created for artistic effect. Art mods are most frequently associated with video game art, however modified games that retain their playability and are subject to more extensive mods (i.e. closer to total conversions) may also be classified as art games. Art mods are usually designed to subvert the original game experience. One example is the Velvet-Strike mod for Counter Strike in which the players spray-paint anti-violence messages in multiplayer games as a form of performance art. Another example is Robert Nideffer's Tomb Raider I and II patches which were designed to subvert the unofficial Nude Raider patch of the late 1990s by altering Lara Croft's sexual orientation. The origins of the art mod can be traced to the classic 1983 mod Castle Smurfenstein (a humorous subversion of Castle Wolfenstein which replaces the Nazi guards with Smurfs). The very first art mod, however, is generally considered to be Iimura Takahiko's 1993 AIUEOUNN Six Features (a modification of Sony's "System G").
Support continuation by mod
After EA lost the license and ended the support for the MVP Baseball 2005, the game's modding community continues the support and releases updated roster lists every year as also alternative leagues (e.g. MVP Caribe, a total conversion).
Released 2011 IL-2 Sturmovik: Cliffs of Dover received mixed reviews due to bugs and other issues. Modders fixed the game over time, got source code access granted, which lead to an official re-release under the name IL-2 Sturmovik: Cliffs of Dover BLITZ Edition.