How to summon and defeat Bonemass in Valheim

Struggling to beat Bonemass in Valheim? This Valheim boss looks a lot like a big version of the bouncy green slime from Flubber, but don't be fooled, it's nowhere near as friendly and may even be the fiercest of the Forsaken foes. It's certainly worth schooling up on how to build a Valheim portal for this guide.

We'll be heading to the Swamp for this battle, so you'll want to spend some time exploring the surrounding area and preparing for the challenge ahead. Leeches, Wraiths, and Draugr roam through this section of the Valheim map, and it's easy to feel overwhelmed quickly. I'm here to help you survive this difficult boss fight. So, here's how to summon and defeat Bonemass in Valheim.
How to summon Bonemass in Valheim

Bonemass lurks in Valheim's Swamp—an unforgiving biome teeming with deadly enemies. You can find Bonemass' exact whereabouts by interacting with a runestone located in the Sunken Crypts. However, you'll need to use the Swamp Key that you got from defeating The Elder boss before you can pry these creepy crypts open.

To summon Bonemass, you need to place ten Withered Bones at the skull altar in the Swamp. Withered Bones can be found in the Sunken Crypts and in large Muddy Scrap Piles.

Valheim Bonemass boss tips: How to defeat it

Bonemass is notoriously difficult to defeat as it's resistant to almost every damage type, with just one exception. Blunt attacks prove to be most effective against this big green monster. Before attempting to take Bonemass on, it's a good idea to craft a Valheim iron mace/sledge, or even a Stagbreaker war hammer. As Chris has previously outlined, even a fully upgraded wooden club will do the trick.

It's also worth crafting poison resistance mead, a concoction that reduces poison damage by 50 percent for ten minutes. For that you'll need:

    Equipment: workbench, forge, fermenter (fine wood x30, bronze x5, resin x10)
    Mead base: poison resistance (honey x10, thistle x5, neck tail x1, coal x10)

One of the most important things to remember about Bonemass is that it can heal, so you need to keep the pressure on and defeat it swiftly. Just like the other bosses, this one has three attacks: a close quarters melee strike, poison AoE gas clouds, and the ability to spawn Blobs (poisonous slimes). After taking a swig of your poison resistance mead, hack at Bonemass with your melee weapon of choice. If you're working with some pals, make sure at least one person is keeping an eye on nearby enemies, you are in the Swamp after all.

If you've already explored the Mountain biome and have a stash of Obsidian, it's possible to deal consistent damage from a safe distance using frost arrows and a Draugr bow. Regular arrows are pitiful against Bonemass, so if you don't have the frost variant, stick to melee weapons for this fight.

YouTuber 04AM has a helpful video outlining the best method. The general idea is to build a narrow staircase on top of the giant skull in the boss arena. You can then stand directly above Bonemass and target his head with the frost arrows. Remember to watch out for Blobs that try to poison you from the base of the stairs, and be sure to build the staircase high enough to avoid Bonemass' poison gas clouds.