On this page of the Valheim game guide, you will find tips related to the boss fight with Bonemass. This walkthrough provides information on how to defeat this boss.
Bonemass is a boss who lives in the Swamp. It is a shapeless creature that moves primarily through water.
While exploring the Swamp (especially the Sunken Crypts), you can come across a Rune Stone which contains the location of the boss. When you interact with it, a marker will be highlighted on the map, showing the nearest summoning altar.
When you arrive at the destination, you must make an offering. In this case, the offering consists of 10 Withered bones. You will find them while exploring the Crypts.
The fight with Bonemass is challenging. He is immune to bow and arrow damage, making long-range combat virtually impossible. Instead, he is vulnerable to melee damage. To be able to attack at close range, make sure you have some poison resistance mead on you.
The boss has three types of attacks. The first is the punch which Bonemass delivers when you are directly in front of him. The second is the emission of poisonous gases. When you notice that he's preparing to release it, you simply have to move away.
The last type of attack is summoning other units - Skeletons and Blobs. The moment they appear on the arena, focus on them and take them out. Like Bonemass, they are susceptible to melee damage.
For defeating the boss, you will receive a trophy which you can use as an offering at the Sacrificial Stones. In return, you will get a power that gives you resistance to physical damage. Additionally, you will also receive a Wishbone It allows you to discover buried materials (such as e.g. silver).