After defeating the elder I found myself procrastinating on travelling to the swamps, tracking down bone mass and ending his sad existence. In the back of my mind I knew I had to do it to progress through the game but I was scared and doubted my ability. I had a full set of iron armor, a strong set of weapons and had ample potions and meads. I was building endlessly, exploring the lands and doing anything to avoid getting the job done. Yesterday before I hopped on the computer I said to myself I'm doing it, I'm killing bone mass, so I started prepping, gathering my potions and food, setting up my inventory for success. The time had come and I was ready to take on the mass. I had a location quite a fair distance from my home base so I set out on my adventure. Black soup, deer stew and meat sauce was my set of food, I had arrived at the alter, heart beating, very clammy hands and my leg was bouncing hard. Dropped in the bones and it was on, I used my bow with iron arrows and it wasn't doing alot of damage, I was worried. Blobs everywhere and skeletons constantly attacking me, I used my stag breaker to clear out the minions that bone mass threw out of his hand and switched my weapon to the mace. I Charged at him, rolling in on the way avoiding his high damaged swipe, hitting him 3 to 5 times surprisingly dealing alot damage. Long story long, I had accidentally used a stamina potion when I wanted to use the poison resistance potion because I was dangerously low on health. I managed to avoided hits from bone mass and archers on the outskirts untill my health was back to normal and I went in for the kill. The battle was long and I was so nervous I felt woozy in the stomach, about 15 minutes later I had him down to very low health, excited, low on health (about 24hp to be precise) took my last swipes and down the mass went. I was so happy and felt very accomplished. Moral of the story, if you find that you're procrastinating about taking on a boss or doing an activity that's hard, just do it because majority of the time you're ready, you're just putting it off.
Source: https://www.reddit.com/r/valheim/comments/uv1aa8/the_demise_of_bone_mass/