City of Villains is both the first expansion for City of Heroes, and a standalone game. In it, you can play a villain, rob banks and fight heroes, all while advancing your own schemes. You can also form Strike Forces to take out heroic threats, create Villain Groups and make hidden lairs and headquarters.
City of Villains is an MMOG, and requires an Internet connection and a monthly charge.
The game has an Arachnos soldier NPC with the name "Jenkins". He usually keeps getting himself captured and you have to rescue him. As confirmed by the game's developer, this is a nod to the Leeroy Jenkins phenomenon from World of Warcraft. You can find out more about it in the related links of the World of Warcraft game entry.
In July 2008 NCsoft announced the complete merger of its City of Heroes and City of Villains titles into one game universe. Current subscribers who only had one of the titles received access to the features of both games, and new sales grant access to both.