Bonemass is the third boss players can fight in Valheim. Unlike the previous two bosses, Bonemass requires a bit of preparation and is otherwise a significant hurdle players will need to overcome.
Where to find Bonemass
To get the Bonemass marker added to your map, you will need to interact with the correct vegvisir. This runestone can be found in the swamp area, specifically in Draugr towers. Look out for towers with an internal stairway; the stone is typically on a sort of balcony.
How to summon Bonemass
Much like how you must offer deer trophies to summon Eikthyr, you must offer a sacrifice to summon Bonemass. The clue on the back of the skull reads “cook their remains”. For those that have taken the time to farm iron, you may have an idea of what you must offer: Withered Bones.
Offer up 10 Withered Bones to summon Bonemass and begin the fight. You can find all the Withered Bones you need inside the Sunken Crypts that are dotted around the swamp biomes.
How to beat Bonemass
As for actually beating Bonemass, this one is going to be the first real struggle for a lot of players. Bonemass is resistant to just about every form of attack (slashing, piercing, etc) but he is especially weak to one thing: blunt. It is highly recommended you spend some time collecting iron to make an iron mace for you and your team. You can even use something like the Iron Sledgehammer if you’ve found the merchant and purchased Ymir flesh.
The other thing to note about the fight against Bonemass is that he does a lot of poison damage and summons Blobs and Oozers. To defend against this, use a cauldron and fermenter to create Poison Resistance Meads. This mead halves how long you are poisoned for and will make this fight significantly easier.
When you have your iron mace, poison resistance meads, and your food, you should be in a good position to summon Bonemass and start hacking.
The Bonemass fight is really inelegant. The only way to damage him is to be right up in its face, swinging with the mace. If you’ve got multiple people, take turns running in and trading aggro while someone hits. The Eikthyr buff will help with stamina consumption as you’re running around.
If you do take too much damage, back off and find a place to heal. A good idea is to put a campfire near some of the large trees that you can't chop down. The little crooks and nooks in these trees actually offer shelter and comfort, which will help get your Rested buff back.
You will also want to be clearing enemies before things get out of hand. Take the time to clear Skeletons, Draugr, Greydwarfs, Blobs and even any Wraiths that might join in on the fun.
When you do manage to defeat Bonemass you will receive a new item called the Wishbone. This can be activated like a piece of armor or the Megingjord and will reveal to you buried riches, like various ores and chests. Remember to put the Bonemass trophy on the Sacrificial Stones to receive the Bonemass ability, which offers resistances against physical damage (blunt, slash, and pierce).
The fight against Bonemass is extremely challenging if you start it ill-prepared. But, bring along a blunt weapon, poison resistance mead, and plenty of food and you’ll be able to not only survive but bash this monstrosity back into the swamps. Be sure to check out the Shacknews Valheim guide for more boss and resource guides.