Vigilante

The Vigilante mission is a vehicle-based side mission in every GTA III Era game 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.

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. (Watch out, they may even steal your car!) As the player completes each level, the target/s come armed with better weapons and, as of GTA: Vice City, become more numerous until eventually, multiple vehicles appear with each new level.

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.

The mission is failed if the player remains outside of a Law Enforcement vehicle for more than 60 seconds in one go, or if the player dies or is busted. Vigilante mode does not grant immunity from the Police, who will often pursue the player for murder, firing weapons, hitting police cars etc. Each time a Vigilante mission is started, the player must begin at Level 1, and cannot continue a previously failed or cancelled mission. In Vice City Once level 12 is reached, your max armour will increase to 150.

In GTA IV, the Vigilante missions are retooled. When Niko parks a police car, he can access the criminal database computer and view crimes in progress in the area. These crimes include gang activity, stolen vehicle, and suspect on foot. In addition, there is a new form of the mission called Most Wanted.

Rewards
GTA III
 * 2 Police Bribes (20 kills in Portland)
 * 2 Police Bribes (20 kills in Staunton Island)
 * 2 Police Bribes (20 kills in Shoreside Vale)

GTA Vice City
 * Maximum armor increased to 150 (complete level 12)

GTA San Andreas
 * Maximum armor increased by 50% (complete level 12)

GTA Liberty City Stories
 * Maximum armor increased by 50% (complete level 12)

Vehicles

 * Barracks OL
 * Enforcer
 * FBI Rancher
 * FBI Truck
 * FBI Washington
 * HPV1000
 * Police Car
 * Ranger
 * SWAT Tank
 * Rhino
 * Hunter
 * VCPD Wintergreen