Quests in the game were known as missions, and were obtained through various channels, generally from various NPCs the player met in the game. Although missions could be completed alone, the player had the option to form Teams with other player characters to play off of each other's characters' strengths and abilities. The level of the characters used, size of the team, and a separate difficulty scale chosen by the player called Notoriety, all affected the difficulty of the mission. Missions could take the form of an instanced area where the player(s) must defeat a boss, save NPC characters held hostage (sometimes taking the form of escort missions), or search the instance for a certain object or number of objects (such as clues or defusing bombs), while other Missions required that players defeat a certain number and type of mobs, possibly in a defined area of the game. Some missions are part of story arcs that involve the player in a larger narrative that tells some of the back story of the setting. Task Forces ("City of Heroes"), Strike Forces ("City of Villains"), and Trials (both) were particular missions that could be completed multiple times, but only as part of a team, and had to be completed in entirety to earn particular rewards for completion, such as the ability to respec a character's chosen Powers and Enhancements.