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Yharnam, Blood Queen of the Old Labyrinth is the end boss of the final Pthumeru Dungeons. You need to go through quite a lengthy process in order to get to her, as you need to complete all the Pthumeru Chalices in order. The first one you get from defeating the Blood-starved Beast in Old Yharnam. The rest, you will obtain from the dungeons themselves.
Pthumeru Chalice (3 layers)
Central Pthumeru Chalice (3 layers)
Lower Pthumeru Chalice (4 layers)
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Defiled Chalice (3 layers)
Completing thesefour chalice dungeons will let you get to the 5th and final one, which houses the Blood Queen.
Pthumeru Ihyll Chalice (3 layers)
Strategies
Boss Video Walkthrough
Bring a lot of antidotes for the fight since her blood attacks can poison you and a weapon that can do damage quickly.
She will start out by spraying poisoned blood around her for damage. Run in close and do two attacks, but be wary of the baby crying because when it cries, it means you can get paralyzed for 5 seconds if you stay too close to the Queen. You also need to look out for her blood explosions when she raises her arms up which she tends to do if you rush her. When she raises her arms, wait until the explosion is about to happen, step back twice, and then attack her.
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After losing 1/3 of her health, she will bring out a dagger she will use to rush you occasionally. She will create multiple copies of herself that fire blood at you but they can be destroyed easily with one attack. The queen will also get attacks such as creating an anti-gravity field that does minor damage, but you can avoid it if you step outside of its perimeter in time.
Her most devastating attacks occur when she puts her blood sword into the ground causing poisoned spikes to erupt next to you so dodge them quickly and heal if necessary. Make sure to attack quickly if the baby is crying near her, but if the baby isn't crying, you can exploit this to attack as much as you can.
