Grand Theft Auto III - The Definitive Edition

This achievement is a bit of confusing.

You need to do this for each island for it to unlock.
20 Vigilanters per island (does not have to be in 1 go)
20 fires estinguished per island (does not have to be in 1 go)
Level 12 consecutively ambulance has to be done in 1 go.

Best and simplest way to do it is at the end of the game with a tank(Rhino)

Weapons you need for this:

Fist
Bat
Pistol
Uzi
AK-47
M16
Sniper Rifle
Rocket Launcher
FlameThrower
Shotgun
Granade
Molotov
Remote Detonator (you get this from mission "i scream, you scream"

Mostly you get to use all weapons from Rampage missions so unless you did not get it through that, then the list is here

Tips if you want to do this early:

1. Collect 20 hidden packages, this will unlock Uzi at the hideout.
2. Stock up ammo by picking up Uzi, save (sometimes twice), repeat. 900-1000 is enough.
3. If possible keep your wanted level at 2 stars, this will help when your police car is destroyed. Learn where the Bribes are, police started to get annoying at 3/4 stars. Getting 10 (and 20) kills will unlock Bribes at the hideout.