DOOM 3: BFG Edition
59 Achievements
50-60h
Cookie Stealer
Defeat Guardian boss in DOOM 3
8.3%
How to unlock the Cookie Stealer achievement in DOOM 3: BFG Edition - Definitive Guide
While dodging fireballs that roll across the ground toward you, shoot the Seekers (with a shotgun or machine gun) which appear 3 at a time hovering above you. With 3 Seekers dead, quickly shoot the blue-light above the Guardian's back with a chaingun or plasma gun. 3 more Seekers will quickly reappear, so you can restart the process 2-3 more times. On the 3rd or 4th attack on the blue-light above the Guardian's back, the Guardian of Hell will die. Then you will receive the Soul Cube, not to mention an unlocked achievement for 15G.
Story related, cannot be missed.
This is the Guardian boss that you will come across at the end of the Hell level. It is very easy to kill and all you need to do is kill the "Seekers" that are flying around. Once all are dead the Guardian will spawn more from it's back. Shoot at the light emitting from its back, when it's red that means you are hurting it.
Story related and cannot be missed.
The Guardian is the boss you must defeat within the Hell levels to gain the Soul Cube weapon.
The absolute easiest way to kill him would be to enter the portal with the BFG equipped and let the cut-scene finish, then let off a fully charged BFG shot right at his blue energy sphere; DEAD. If he doesn’t die, continue the fight like described below.
However, if for whatever reason this doesn’t work for you, then this is the second best way: try to utilize the pillars and corners as cover and shoot down the “seekers” first. They look like flying squid things with flashlights. Once you kill these, aim for the huge energy type sphere above the boss itself and you should have no problem defeating it.
Here is a video of the battle by AlanWilderDM: