How to summon Valheim Bonemass boss and defeat them

In Valheim, Bonemass is the tanky Swamp boss that must be summoned before you can fight him. After defeating the Valheim Elder summon, you'll be faced with this far more treacherous boss fight, so you'll need to come prepared with the best Valheim weapons for the job. It might take some tips, tricks, and nimble skills to back it all up, but defeating Bonemass can be done.

As one of the most elusive big bosses in Valheim, be prepared to put a lot of work into tracking him down. As with every boss you must summon, your first task will be finding Bonemass’ Sacrificial Altar and summoning materials. You're not on your own, though, because our Valheim Bonemass guide gives you all thinfo you'll need to bring him down.

1. Bonemass location in Valheim

The Bonemass sacrificial altar is somewhere in the Swamp biome. His exact location on the map will be revealed by a location Runestone, which you can find in the Swamp biome as well. They often spawn in Sunken Crypts or next to Draugr buildings. 

After activating a Runestone and making your way to Bonemass’ sacrificial altar, you need to offer some materials before he appears. The materials needed to summon Bonemass are 10 Withered Bones. 

2. How to find Valheim Withered Bones

The Valheim Withered Bones are found in Muddy Scrap Piles or chests inside the Sunken Crypts in the Swamp Biome. It’s very hard to find Muddy Scrap Piles outside of the Sunken Crypts for now, as you don’t have any indication of where to dig. This will change after you defeat Bonemass, when you get the Wishbone as a reward.

Luckily, you already have the Swamp Key as a reward for defeating The Elder. You can simply explore Sunken Crypts until you have enough Withered Bones to summon Bonemass. Clearing merely one Sunken Crypt is likely enough to get you at least 10 Withered Bones (provided you break all the Muddy Scrap Piles inside). Don’t forget to bring your pickaxe!

3. Summon Bonemass fast with this Valheim world seed

Still have trouble finding the Valheim Bonemass boss? Then use this World Seed to spawn on the map in the picture: RtE9ytMifX. If you already used this Seed to find Eikthyr, you can immediately run towards Bonemass from Eikthyr’s location. 

If you don’t have enough materials to summon Bonemass yet, go to the location of the red dot first. You will find plenty of Sunken Crypts with location Runestones and Withered Bones in this area. One more tip before you set off to fight Bonemass: take a boat to avoid the dangerous Plains biome. If you look closely at the map, you can see that most of the route allows travel over water.

4. How to defeat Bonemass in Valheim

The best strategy to defeat the green pile of blubber that is Bonemass, is by attacking him with blunt weapons. A mace or hammer-type weapon such as the Stagbreaker will suffice. Check the stats to make sure the weapon of your choice does indeed do blunt damage, and consider upgrading it several times before starting the battle. 

Furthermore, as it’s hard to keep your distance when fighting this boss, make sure you have good armor too. Especially if you’re playing solo - you might want to craft some Iron Armor first, using the Iron Scraps you found in the Sunken Crypts. 

Finally, you should know that Bonemass can poison you. You remove a big part of the problem by using a Poison Resistance Mead. This potion will decrease the amount of poison damage your character can take, lasting for 10 minutes.

5. Bonemass Forsaken Power

Like other Valheim bosses, Bonemass will drop a Trophy to hang at his stone altar (default world spawn point). Apart from looking cool, you can use the trophy to activate Bonemass’ Forsaken Power. If you use it (press ‘F’), you will gain increased resistance against all physical damage. Bonemass will also drop the Wishbone, which can be used to find buried treasures.

On to the Mountain biome & Moder next!

Ready for more big boss battles? Here's how to defeat Valheim Moder and Valheim Yagluth.