The Mausoleum of Evil is the first main mission of the sixth region in NiOh 2. This page of the guide contains a walkthrough for this mission.
After praying in the first shrine, head straight ahead - you will meet an NPC called Mumyo. Talk to her and then pick up items. There is a broken bridge on the right, and there is a statue of a dragon near the bridge. You don't have an item that you can put into the statue to lower the water level in the location yet. Go up instead.
As you go up, you will encounter a patrolling Dweller. Another one is near the corpse on the stairs. Defeat them and go up the stairs.
You will encounter Ubume holding an Amrita crystal - attack this crystal to inflict heavy Ki damage. A Yokai soldier is on the other side of the bridge. Deal with them and jump one floor down by the bridge.
At the bottom, go left - you will find a Kodama around the corner.
Going even lower, you will notice, among other things, a large Snowclops. Head towards him. Be careful, though, because there is a Dweller at the top of the building - he will throw bombs at you.
Cross the small bridge and defeat a Yokai soldier. Don't climb the stairs to the top yet. Instead, you should go forward - there will be a tree on the right side that you can topple to unlock the shortcut to the shrine.
A large Amrita crystal is inside the building behind you. Don't go there for now, because you will have to face a Tengu and a Yokai soldier. Instead, go up the stairs on the left (the place where you fought a Yokai soldier). You will find a small chest upstairs. Go inside the building where you will have to fight Nure-Onna and a Dweller.
When you beat them, jump down and start attacking the crystal, the enemies shouldn't even notice you. By destroying the crystal, you will kill nearby opponents. You also get the orb that you have to put inside the dragon statue to lower the water level in the location.
Destroying the crystal will create a hole - jump into it. But don't do it now. First, go back to the dragon statue and put the orb inside it.
Cross the wooden bridge and go slightly to the right - you will find a ladder. Be careful, though, because there is a Nure-Onna hiding at the top, near the ladder. Shoot her down and finish off. Then climb up the ladder.
Inside the building, you will find a Sudama on the left, and a Scammpus on the right. Get out of the building and go left - you will encounter a Dweller. Kill him and keep going. Reach the end of the path to find a Kodama.
After picking it up, jump down and walk to the gap that is next to the ladder. There you will encounter a lesser Umi-Bozu. After defeating it, jump down to the lower levels of the building.
There is a Cyclops at the bottom - defeat him to purify the location from the Yokai Realm. Be careful, however, because by jumping off, the enemy will likely perform a Burst Attack immediately.
Start the fight by shooting him in the eye to stun him for a moment. This should make the fight a little easier. Once you have beaten him, climb up the ladder. At the top, you have a chest and a Dweller. There is a wooden roof on this level that you can jump on by dodging at the right moment. You will jump on the wooden beams.
Ubume nearby guards the chest, while on the other side you have a Yokai soldier. Go towards the soldier and turn left - you will go outside. You will encounter a larger Dweller there. Defeat him and go around. Go back to the place where you fought Cyclops and climb the ladders to the top.
Once you reach the top, you will find a path on the right, where the corridor ends. First, however, turn left and climb the next ladder. There you will find a chest. The Yokai mist in front of you will spawn a Tengu. You have limited room, so watch out for its spinning attacks. After defeating him, open the door in front of you.
This will unlock a shortcut. Step back and reach the end of the hall and descend the ladder down. That's where you will find the way down. However, beware of opponents who will block your path. Try shooting them down from a safe distance.
Later, you will encounter a lesser Umi-Bozu - attack this enemy with fire. You can see another crystal at the top, but to reach it, you have to follow the path on the right. Be careful, though, because there is a Dweller hanging on its edge. After defeating him, jump down to the stone floor.
The aforementioned crystal will be in front of you. It is guarded by Nure-Onna - defeat her and then take care of the stone. Pick up all items that fall out of the crystal, - you will get the Dragon God Jewel, which must be inserted into the next dragon statue.
Jump down and you will see Nurikabe on the right. Deal with this enemy. Behind him, you have another lesser Umi-Bozu. Keep moving forward - you will find loot. Jump down - there's a dragon statue right in front of you. Interact with the dragon. The water level will drop again, unlocking access to another part of the location.
Jump down, there is a Sudama on the right. You have another shrine in front of you.
Head down to the central chapel and you will encounter Namahage on the left and a Yokai soldier on the right. Take care of the soldier first - he is easier and faster to kill than Namahage. After that, deal with the other enemy. There are several passes around - go to the first one on the left.
Go to the top and defeat a Dweller. Pick up the object laying nearby. You can enter the building on the left. The Yokai mist inside will spawn an Ubume. But before you engage in a fight with Yokai, open the chest on the left.
After defeating the enemy, go around the building and you will find a Kodama. Go up - there is a road on the left that leads to the previously unlocked dragon statue. Go back to the room where you fought Namahage. Go to the right where you defeated a Yokai soldier. Jump down and defeat a Dweller.
After defeating the Dweller, cross the small bridge and head to the next room. There is a chest on the right. Go left to continue exploring the location.
There is also a Kodama on the left, but don't go to it - the Nure-Onna at the very top of the room will jump on you when you get close enough.
Defeat the enemy, interact with the Kodama and continue your journey. You will encounter more opponents in a moment - one smaller and one larger Dweller. After beating them, go up the ladder. Now you have several paths to choose from. One leads down the ladder, where the opponent is a lesser Umi-Bozu, while the other leads to a large building with several opponents inside.
First, enter the building - you will encounter a Yokai soldier. He is standing with his back toward you. Beat him, pick up the items, and go to the next rooms. There is a ladder on the right side - climb to the top.
The Cyclops on the upper floor guards a large crystal. The advice is that you don't have to fight Cyclops - destroy the crystal to kill the enemy. If you prefer easier solutions, run quickly behind Cyclops' back and attack the crystal, while making sure that Cyclops doesn't attack you. By destroying the crystal, you will receive another Dragon God Jewel. After picking up the key item, go down the stairs, and turn right. Descend the ladder.
Downstairs, you will encounter Nure-Onna and Nurikabe. Take care of Nure-Onna first, then approach Nurikabe and make the right gesture.
The passage leads to the roof, where you will find an item and a Sudama. The creature is located slightly below, on the roof to the right. Jump down and face Ubume.
She holds Amrita in her hands - shoot it to greatly weaken her Ki. After defeating Ubume, go to the next dragon statue located in the center.
Place the Dragon God Jewel in the statue. The water level will start to drop again - jump down. Watch out for the lesser Umi-Bozu, if you haven't killed him yet.
Once you go down, keep moving to the arena. Watch out for the Yokai mist - a Tengu will emerge from it. The arena is large, so you have plenty of room to dodge, but be careful not to fall into the water - this will kill you instantly. After defeating the Tengu, go to the top.
Going up the stairs, you will reach the arena with the boss. Don't go there, though. First, turn left and go down - you will encounter a Cyclops. Defeat him and jump down again. You will reach Yokai Realm.
Don't go down the ladder, go around. Next you will encounter Nure-Onna. After defeating her, you have to cross the small bridge and watch out for Namahage and the lesser Umi-Bozu that hangs from the ceiling. Namahage is the cause of the Yokai Realm in this location. Defeat him to remove the Yokai mist.
Notice the lever in the room with Namahage - it rotates the small bridge, unlocking the shortcut to the boss. Pull the lever and cross the bridge.
Jump down to the arena you have visited before and then go up again. Once you are at the top, visit the previous shrine and rest. Now you can proceed forward because you have unlocked the shortcut to the boss. Keep moving forward until you enter a building with a single large Dweller. You will also find a Kodama there.
It's around the corner on the left - you have to turn around. Defeat the Dweller and go straight to the boss arena - it is behind closed doors. The boss is Shuten Doji - a strategy for this fight can be found on a separate page.