Vigilante

The Vigilante mission is a vehicle-based side mission in every GTA III Era game, Grand Theft Auto IV, and Grand Theft Auto: Chinatown Wars in which the player is required to chase down and kill the indicated targets (other criminals) within a time limit. Vigilante mode can be activated at any time (when not already in a mission) from within a Law Enforcement vehicle, such as a Police Car).

Brown Thunder is a (technically) separate but more or less identical side mission, which can be activated from a Hunter attack helicopter in the games in which that vehicle appears.

GTA III era
At the start of the mission, a criminal spawns in a random vehicle (clearly marked and shown on the radar) and attempts to evade the player. If the vehicle catches fire or is held in place for more than a couple seconds, the occupant(s) will bail out and run or attempt to acquire new transport. They may even steal your car! In GTA Vice City, a new car will spawn for the criminals to use if the player doesn't kill them fast. As the player completes each level, the target/s come armed with better weapons and, as of Grand Theft Auto: Vice City, become more numerous until eventually, multiple vehicles appear with each new level. In Grand Theft Auto: San Andreas, criminals will have the ability to drive-by. The player has to be ready to flee as well, since some of the criminals come very heavily armed with, for example, Rugers and Shotguns that can, and will, kill both the player and their car in seconds.

Aside from the obvious choices of drive-by shooting the target vehicle until it blows up or ramming it off the road, there are other options. For example:
 * Performing the PIT maneuver to spin the vehicle out and then successfully blocking it will prompt the target/s to abandon the vehicle, allowing you to engage them in a firefight or simply run them over.
 * Identifying the target vehicle's likely route (only a practical option in some areas with few side roads) and setting up an ambush or roadblock ahead of it. Using a powerful weapon, it is very possible to blow up their car before the assailants have time to get out of it.

The mission is failed if the player remains outside of a Law Enforcement vehicle for more than 60 seconds in one go, if the player dies or is busted, and of course if the time runs out. Vigilante mode does not grant immunity from the Police, who will often pursue the player for murder, firing weapons, hitting police cars etc. They make it a lot harder since almost no emergency vehicles can be resprayed, and you might rack up your wanted level faster than you can find police bribes.

Each time a Vigilante mission is started, the player must begin at Level 1, and cannot continue a previously failed or canceled mission. GTA Vice City Stories has a checkpoint every five levels so you can restart at that checkpoint if you failed or canceled before completion.

GTA IV era
In GTA IV and GTA Chinatown Wars, the Vigilante missions are retooled. When Niko or Huang accesses a police car, they can access the criminal database computer and view crimes in progress in the area. The player has a time limit to get to the crime scene, but once there the timer stops. These crimes include: Gang activity, which involves killing a group of thugs; Stolen vehicle, which involves chasing down the criminal in the stolen vehicle; and Suspect on foot, which consists of only one criminal fleeing a crime scene, and are usually the easiest, as the criminal can simply be run over. In GTA IV, 20 missions must be completed for the Cleaned The Mean Streets Achievement and for 100% completion. The 20 missions however do not need to be done consecutively. In addition, there is a new form of the mission called Most Wanted. In GTA Chinatown Wars, the side-mission automatically ends when you kill the last criminal on each wave, and to restart it you must reenter a Law Enforcement vehicle and access the Police Computer, so you don't have to beat all five waves consecutively to obtain the Gold Medal, as long as the chain is completed without failure.

Rewards
Grand Theft Auto III
 * +1 Police Bribe at the Hideouts (Total 10 Kills in Portland)
 * +1 Police Bribe at the Hideouts (Total 20 Kills in Portland)
 * +1 Police Bribe at the Hideouts (Total 10 Kills in Staunton Island)
 * +1 Police Bribe at the Hideouts (Total 20 Kills in Staunton Island)
 * +1 Police Bribe at the Hideouts (Total 10 Kills in Shoreside Vale)
 * +1 Police Bribe at the Hideouts (Total 20 Kills in Shoreside Vale)

Grand Theft Auto: Vice City
 * Maximum Armor Increased by 50% (Complete Level 12)

Grand Theft Auto: San Andreas
 * Maximum Armor Increased by 50% (Complete Level 12)

Grand Theft Auto: Liberty City Stories
 * Maximum Armor Increased by 50% (Complete Level 12)

Grand Theft Auto: Vice City Stories
 * Maximum Armor Increased by 50% (Complete Level 15)

Grand Theft Auto IV
 * Cleaned The Mean Streets Achievement/Trophy
 * Manhunt Achievement/Trophy

Grand Theft Auto: Chinatown Wars
 * Maximum Armor Increased by 100% (Get Gold Medal)

GTA III Era

 * Barracks OL
 * Enforcer
 * FBI Car
 * FBI Rancher
 * FBI Truck
 * FBI Washington
 * HPV1000 (bike)
 * Police Car
 * Ranger
 * Rhino (tank)
 * Hunter (helicopter)
 * SWAT Tank
 * VCPD Cheetah
 * VCPD Wintergreen

GTA IV Era
The following vehicles can initiate missions:


 * FIB Buffalo
 * NOOSE Cruiser
 * NOOSE Patriot
 * Police Patrol (GTA IV / GTA Chinatown Wars)
 * Police Cruiser (GTA IV)
 * Stockade
 * APC
 * Police Stinger ( GTA: TBoGT Multiplayer)
 * Police Bike (GTA: TBoGT Multiplayer)
 * Police Buffalo (GTA: TBoGT Multiplayer)
 * Brickade

The Enforcer, Annihilator and Police Maverick can be used to continue missions after they have been initiated in another vehicle.