The Berserk Hunter is the second boss in Doom 3: Resurrection of Evil. It guards the monorail that the player is intending to take from the Erebus Complex to Phobos Labs. The Berserk Hunter has a large, mouthless head with four small eyes, holes on its knuckles that hide large claws and has normal humanoid legs compared to the Hell Knight's digitigrade, goat-like legs. It is also noticeably larger than a Hell Knight, and stands a full head taller.
The second Hell Hunter, Berserk is extremely fast with powerful melee attacks. Its attack method encompasses two phases. First, it invokes its Berserk ability (denoted by a rise of flames around it) before making a series of leaping attacks at the player. It is while it is Berserk that it exposes its heart and becomes vulnerable. You must use the Helltime power of the Artifact to slow it down once it becomes Berserk and attack its heart
Note: It is strongly advised to have the Artifact already equipped before triggering the Hunter's entrance. He will leap at you as soon as you regain control, and you will need to invoke Helltime immediately to be able to avoid it.
It is only necessary to attack its heart enough to make it react and break it out of its Berserk phase; you can stop attacking once this happens to conserve ammunition. The Double-barreled shotgun, Machine Gun, and Chaingun will all provide the needed firepower to wound the Hunter, so choose whichever works best for your given situation. If you attack it enough just as it finishes its Berserk invocation and first opens its heart, you can preempt the leaping attack, but even if the leaping attack is not stopped, Helltime is the only way to actually dodge the attack, and you will still have time to attack once it finishes its leap.
Once its Berserk attack finishes or is broken, the creature will become invulnerable again and go into its second phase. It will leap back, keeping its distance from you, and charge up and throw a large fireball at the Marine. It will do this 3 times in a row before returning to its Berserk attack phase. The fleshy growth pillars in the room can be used to defend against the fireballs. The fireballs can also be dodged by strafe-running.
Once the player inflicts sufficient damage on the Berserker's heart (which is typically about during the Hunter's third Berserk cycle if the player is using the Chaingun and time dilation), it will die, at which point the Artifact will absorb the Hunter's Berserk power. A much more powerful version of the original Doom's berserk pack item pickup or Doom 3's Berserker, the Marine can punch hard enough to kill all non-boss monsters with one punch, the force sending them flying off their feet. Unless the Marine has to kill an enemy at a distance, using the berserk fist (called with 1, toggling with the Grabber) with the Helltime should prove extremely useful.
Doom 3: Boss FAQ - posted by D00MBuggy.