This walkthrough covers the plot and gameplay of Chapter 21 Final Battle in DOOM The Dark Ages, aiding you in completing the intense chapter.

After being resurrected, the Slayer invades Kreed’s ship and kills Bishop Kreed. Meanwhile, Prince Ahzrak, empowered by the Heart of Argent, launches a devastating attack on Sentinel. As massive titans and an Enhanced Ahzrak invades, DOOM Slayer and King Novik prepare for the final battle to save the Sentinels and Thira. Chapter 21 Final Battle features two epic boss fights — a high-octane Atlan boss fight and a long-awaited encounter. Get the complete walkthrough of DOOM The Dark Ages Chapter 21 Final Battle here.
Related: 5 Things To Know Before Playing Doom: The Dark Ages
Final Battle Full Chapter Walkthrough in DOOM The Dark Ages
Destroying the Hellgate Generators

The chapter starts with Prince Ahzrak and his massive titans invading the Sentinel’s base. Since the Slayer’s Atlan is not fully prepared for the battle, King Novik offers his Royal Atlan to the Slayer instead. Unlike the previous Atlan, this one features a special finisher called ‘Siege Breakers’, which deals massive damage and destroys armor.
Locate and destroy three Hellgate Generators while dealing with the titans. You will also receive a mini-gun through the weapon deploy pod near one of the generators. Upon defeating the titans, interact with the Hellgate Generators to destroy them.
Defeating The Old One

After destroying the three generators, head to the objective marker and break the barrier. While continuing along the way, a cutscene will trigger and introduce the Atlan boss, The Old One. During the battle, the boss opens portals and launches tencacles. Additionally, it also teleports to different locations, making it challenging to hit. Mastering the perfect dodge greatly helps you in taking out the Atlan boss. Upon defeating the Old One, you will encounter an enhanced version of Prince Ahzrak.
Defeating Enhanced Ahzrak

The boss fight with Enhanced Ahzrak features three phases. It is undoubtedly one of the toughest fights you encounter in the game. Landing successful attacks builds up the purple bar below Ahzrak’s HP. Filling the meter causes him to stagger, allowing you to perform the Glory attack.
In Phase 2, he enters his demonic form and gains new attacks. Defeating him on the second phase triggers a cinematic where the Slayer’s mecha dragon comes to save him, but unfortunately killed by Ahzrak. This triggers a Phase 3, which marks the last round of the battle.
Upon defeating him on Phase 3, a cinematic shows the Slayer retains the Heart of Argent from Ahzrak. This creates a massive energy surge from Thira, causing an explosion, providing an opportunity for the wounded Ahzrak to flee. The Slayer then hands over the Heart of Argent to King Novik. He uses it to save Thira, allowing her to regain her powers.
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