Bonemass Boss Guide: Beat the Swamp Wall in Valheim

Bonemass, the third boss in the boss order, is where Valheim stops forgiving sloppy preparation. A writhing mound of bones and muck, he summons adds, floods the arena with poison, and shrugs off most of your iron weapons — unless you bring the one damage type he’s soft to.

How do you summon Bonemass?

Sacrifice ten Withered Bones at his skull altar in the Swamp. Withered Bones come from the muddy scrap piles inside Sunken Crypts — the swamp’s dungeons, which stay locked until The Elder drops the Swamp Key. You can also get bones from Swamp chests and from mining scrap piles directly, but crypts are the reliable farm. Bonemass’s altar is a giant bleached skull on solid ground; find the vegvisir runestone inside a crypt to mark it on your map.

What are Bonemass’s stats and attacks?

Bonemass has 5,000 HP — a big step up from The Elder’s 2,500 — and he is weak to blunt and frost damage. Pierce and fire are heavily resisted, slash is resisted, and he is flatly immune to poison.

Attack	Damage	Notes
Bone swipe	80 Blunt + 50 Poison	Melee reach; the poison is the killer
Poison cloud	130 Poison	AoE around him — step out fast
Summon	—	Spawns skeletons and blobs on a timer

The adds make the fight snowball: ignore them and the arena fills up, chase them and he regains tempo.

What is the best strategy against Bonemass?

Drink poison-resistance mead before the pull — it is the single most important prep item in the entire game. A cauldron-brewed poison mead turns his scariest numbers into survivable ones. Fight with an iron mace (the S-tier blunt pick of the tier) or frost arrows, kite his swipe, and kill summoned blobs before they stack the poison debuff. Eat a health-weighted food rotation per the food tier list — sausage-era meals carry the fight. Clearing trees around the altar gives you room to dodge; many players flatten the area before summoning.

What does Bonemass drop?

The Wishbone, a Bonemass trophy, and his Forsaken Power. The Wishbone pings buried silver veins and treasure — it is how you find silver once you reach the Mountain. His trophy power grants physical damage resistance (-25% to blunt, slash, and pierce) plus free, stamina-refunding blocks for five minutes — the tankiest defensive power in the game, and the default pick for hard fights like Yagluth afterward. Killing him also unlocks swamp-themed raid events — check the events and raids guide before your base gets a visit.