DOOM: The Dark Ages Guide | Final Battle - All Collectibles, Secrets, Upgrades & Challenges

At the beginning of Mission 21 (Final Battle), you'll be rewarded significantly for maintaining your kill combos between combat zones. If you can fill up the full combo ring, you unlock a powerful gun attack that behaves like a plasma cannon and instantly destroys any enemy it hits.

Carrying this combo into each area makes the mission dramatically easier and faster. If you lose your combo often, the mission may take two or three times longer.

Move from area to area, clearing each checkpoint as efficiently as possible. Your goal is to destroy three Hellgate generators. At each generator, you'll fight a small group of enemies, receive a weapon boost, and continue toward the next zone. There are no mission or weapon challenges here, so you can focus purely on combat efficiency and survival.

The Old One Boss Battle

After clearing all three generators, you transition into the first phase of a boss fight against The Old One. This is an Atlland-versus-Atlland battle. Stick to what you've already learned. Keep your combo alive, and use your siege cannons whenever possible. This is the third attack in your arsenal and crucial for damage output.

If you do extremely well, the boss's health bar may hit zero while it still remains active. This is likely a scripted encounter, so continue attacking until the required animations or attack phases finish.

Enhanced Ahzrak Boss Battle – Phase 1

You now move on to Enhanced Ahzrak, a multi-phase boss fight. Start by using the combat shotgun. This helps you learn the boss's patterns, land frequent parries, and even ignite Ahzrak to make it drop health. Stick to the outer edges of the arena to gather armor and healing items.

The chain shot is a solid choice throughout this fight due to its consistent effectiveness. While the rocket launcher deals more damage, it can be difficult to land hits with. The ballistic crossbow doesn't deal much damage, offers no ammo refills, and becomes inefficient quickly.

When the boss is stunned, you may feel tempted to use a melee attack. Be aware, though, that the melee animation often pushes you away and doesn't inflict real damage. You can use the dread mace, too—it performs well when you land a few parries and recharge it mid-fight.

Watch out for red priest walls that float toward you. Destroy them quickly before they reach you, as they can empower Ahzrak or deal heavy damage.

Enhanced Ahzrak Boss Battle – Phase 2

In the second phase, Ahzrak gains wings and new armor. Occasionally, he spawns superheated metal spikes. Throw your shield at these as soon as possible to prevent them from detonating. If left alone, they cause fire damage and may provide Ahzrak with a shield that prolongs the fight.

Focus on parrying attacks whenever possible. Not only does this reduce damage, but it also stuns the boss and opens up attack windows. When Ahzrak is weak, melee him to progress the fight.

If you still need to work on the Impaler weapon mastery, this phase gives you some opportunities—though it's unclear whether headshots truly register on the boss.

Enhanced Ahzrak Boss Battle – Phase 3

In the third and final phase, Ahzrak gains even more attacks. He might fly upward and summon red statues that encircle you. You'll get visual and audio cues indicating where the statues are about to strike. Parry them quickly to avoid damage.

After the statues finish their sequence, Ahzrak lands in the center. Green spike projectiles will follow. Parry these to send them back at him, and continue attacking with your preferred weapon. The chain shot remains highly effective. If you need quick healing, switch to the combat shotgun during breaks in his attack pattern.

You can use the ballistic crossbow for quick damage dumps, even if it doesn't deal much. Just keep laying into the boss and landing parries until you drain the final health bar.

Ending the Mission

Once Ahzrak is defeated, you transition into a final cutscene that leads directly into Mission 22. There are no collectibles or side objectives to worry about in Mission 21, so you'll get your 100% chapter completion screen right away.

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