As City of Villains is an expansion to City of Heroes as well as its own standalone title, it features several changes that are unique to its players, unless they also have a copy of the original game. One of the primary changes to the game was the ability to play as a supervillain, with new Archetypes (classes) and powers unique to Villains. Other changes to the game include:
  An instant-access mission system.
  Player vs Player areas for hero vs. villain conflict. This addition was an expansion on CoH's Arena areas, which allowed for Hero vs. Hero battles. Villain vs. Villain is also available in the game.
  Sharper and more detailed graphics, ragdoll physics, and other visual improvements.
  Ability to create/access Super Group bases (this is needed for creation and access to City of Heroes bases also).
These features have been implemented into City of Heroes, as well. The use of a lair in City of Heroes requires a joint-subscription with City of Villains or the Good vs. Evil Edition pack that includes both games. The instant-access mission system is the Newspaper and Broker system in City of Villains. This was implemented in City of Heroes in the Issue 8 expansion as the Police Band system.
Missions
The player's initial tutorial is "Breakout" (the name of which is the inverse of City of Heroes tutorial, "Outbreak") where their character must escape from prison (specifically Zigursky Penitentiary, "The Zig," located in Brickstown) to go to the Rogue Isles, where the majority of the game takes place. After this point, the player gains missions both from the new Newspaper system and from more traditional contacts.
The game has diverse missions which have objectives such as bank robberies and kidnappings, in addition to the mission types currently available in City of Heroes. Players are able to choose between the different types of missions offered by the newspaper. Another type of mission is the Supergroup mission, where your entire Supergroup will be able to take on a difficult challenge. Also, since the release of Issue 7 'Destiny Manifest', players can participate in Mayhem Missions, where villains travel to instanced areas of Paragon City and harass citizens, rob stores, destroy property, and cause general mayhem for a limited amount of time.
Player vs. Player
One major focus of City of Villains is the expansion of Player versus player (PvP) combat. Although PvP was introduced to City of Heroes prior to the release of City of Villains through the Arena combat system, CoV substantially expands the variety and importance of PvP combat.
Three new modes of PvP are included in the expansion:
  There are specific PvP zones which both villains and heroes are able to enter in order to fight each other. These zones contain special objects which provide certain benefits to whichever side is in control of the map. Some of these zones allow open PvP, where players can attack any other player, while other zones allow faction-based PvP, where heroes can only attack villains and vice versa.
  For a short time, Items of Power were available after a supergroup completed the Trial of Pain. If a Supergroup's base contains an Item of Power, the lair is open to (scheduled) raids by any other Supergroup. Items of Power confer modest bonuses upon all members of the owning supergroup
  Players may earn gladiators by accumulating gladiator badges. These gladiators act as proxy fighters for the new gladiator mode of Arena combat.
At the moment, there are four PvP zones; Bloody Bay, Sirens Call, Warburg, and Recluse's Victory.
Bases
Players can create bases for their villain groups. These allow the player to meet-up with other players privately and gain access to useful game facilities. From a base, players can travel directly to specific zones, buy Enhancements and Inspirations, or acquire missions, for example.
Additionally you can store collectable "Items of Power" here. These items provide the group with special enhancements, but also opens up the base for raiding (see also "Player vs. Player" above). The bases can be equipped with traps and other countermeasures to help fend off these raids. During scheduled base defense time periods any other supergroup will be able to raid the base and attempt to seize an Item Of Power.
In order to construct a base, the members of the supergroup must acquire in-game currency known as Prestige. Prestige is earned by members of the supergroup when they play their characters in "Supergroup mode." It is then spent to buy rooms, place items, and pay upkeep expenses for a base. Additionally there is a form of crafting using "Salvage" acquired from defeated NPCs. With Salvage and a worktable placed in a base, you can create various items such as more powerful hospitals or turrets. These placed items can make your base less vulnerable to attack, provide additional functionality for your Supergroup, or increase the visual appeal of your base.