Bonemass

1:29 Bonemass is the third of the eight Forsaken bosses in Valheim and the boss of the Swamp. It is a hunched, dripping green mass of bones and viscous ooze with 5,000 health, summoned by placing ten Withered Bones on a giant glowing skull altar somewhere in the mire (Valheim Wiki). It fights with a poison cloud, a heavy swipe and lumps of itself that hatch into skeletons and blobs, and it is the only boss in the game that is weak to blunt damage. Killing it drops the Wishbone, the accessory that reveals silver veins in the Mountain, and its trophy unlocks one of the Forsaken Powers. Before it come Eikthyr and The Elder; after it, Moder.

Quick facts

Finding the altar

23:11 The Bonemass altar is a huge skull, half-sunk in the swamp, with a boiling pool of green slime in front of it. Its position is marked on the map by reading a Vegvisir, a rune stone that points to the nearest altar of its boss. For Bonemass the Vegvisir stands beside ruined Swamp Runestone Towers or hides inside Sunken Crypts, sometimes on the wall of a treasure room (Valheim Wiki). Because a Vegvisir only reveals the altar closest to itself, the marked skull may lie in a different swamp from the one the player is standing in.

12:00 Summoning costs ten Withered Bones. They come from the Muddy Scrap Piles inside Sunken Crypts, the same piles that yield scrap iron, and occasionally from chests in the swamp (Valheim Wiki). A player who has cleared enough crypts for an iron kit will usually have the ten bones without looking for them; since the Call to Arms Update the bone also has a second use, as an ingredient in the Nimble Anklet trinket (5 Iron, 5 Withered Bone and a Surtling trophy at the Forge) (Valheim Wiki).

Attacks

1:52 Bonemass has three attacks, all close to the ground. It reaches into its own body and throws a lump that spawns up to four skeletons, skeletal archers or blobs where it lands; it vomits a poison cloud around itself that cannot be blocked or dodged, only walked out of; and when a player is close it swings a slow, heavy arm that can be blocked, parried or dodge-rolled. The figures below are from the Valheim Wiki.

3:49 Its resistances turn the usual Viking toolkit upside down. Bonemass takes half again as much damage from blunt and frost, normal damage from lightning and spirit, half damage from slash, and only a quarter from fire and pierce; it is immune to poison and cannot be staggered. Swords, axes, spears and ordinary arrows are therefore poor choices, while a mace, a sledge or frost arrows are the right ones (Valheim Wiki; Physgun boss checklist).

Preparation

5:49 The fight is as much about the arena as the boss. Guides recommend leveling the ground around the skull with the hoe so there is room to move and no water for leeches, clearing wandering Abominations and Draugr first, and going in by day, rested, on the best stamina food available; see Rested, Comfort and Sleeping and Weather, Cold and Wet for why the permanently wet swamp punishes stamina. Poison Resistance Mead is close to mandatory; the Root Mask made from Abomination roots adds its own poison resistance, and the Root Harnesk resists the pierce damage of Draugr and skeleton arrows (Mead and Potions, Armor and Capes). The standard weapon is the Iron Mace, with an Iron Buckler or Banded Shield for parrying and an Iron Tower Shield for players who prefer to block (Weapons and Shields).

Fighting Bonemass

2:18 The straightforward method is melee. A parried swipe leaves time for three or four mace hits before the next attack; more than that and the wet-swamp stamina drain becomes the real enemy. When the poison cloud comes, the player runs out of it and waits for the boss to follow. Summoned skeletons and blobs are killed as soon as they appear, because the fight becomes far harder with several enemies on the field. A player with fully fed stats, iron armor and the mead almost shrugs off the poison, and a level-one mace is enough to win because of the blunt weakness (Combat).

5:19 The oldest alternative is the treehouse. The large non-ancient trees of the swamp cannot be damaged and serve as a foundation (Building and Structural Integrity), so a roofed platform built into one above the reach of the swipe lets an archer shoot without ever being hit. It is slow: wooden arrows do about ten damage against the pierce resistance, Bonemass slowly regenerates health, and one demonstration took 22 minutes and 580 arrows.

10:10 Frost arrows change the sum. Obsidian and Freeze Glands are Mountain materials, but a player in iron gear can fetch them with Frost Resistance Mead, and each frost arrow hits Bonemass for 50 to 60 damage; the same treehouse kill took 77 of them (Bows, Crossbows and Arrows).

11:36 A blunt two-hander from height is faster still. Standing on top of the skull, a player can swing the Stagbreaker down onto Bonemass and its summons while regenerating stamina between swings; the Iron Sledge, which needs Ymir Flesh from Haldor, does roughly twice the damage. A stack of logs against the skull, just above the swipe's reach, does the same for a mace.

12:47 The cheapest cheese uses the boss's poor eyesight: a three-by-three floor built at head height beside the altar, hidden under after summoning, makes Bonemass wander over without attacking, close enough to be hit from cover. Sitting on a chair placed against a tree clips the player inside the trunk with the same effect.

Drops and the Wishbone

13:13 Bonemass always drops its trophy and one Wishbone for each player in the fight. The Wishbone goes in the accessory slot, where it excludes the Megingjord and the Wisplight, weighs almost nothing and has no durability. When worn it pulses with a chime and a puff of green light that quicken as the wearer nears a hidden object, starting about 20 meters away; when the pulse becomes a strobe the player is standing on it and digs. It finds three things: the Muddy Scrap Piles buried in the swamp, which are a second source of iron outside the crypts (Metals and Smelting); buried treasure in the Meadows; and, above all, the silver veins under the snow of the Mountain, without which the next tier of gear cannot be made (Valheim Wiki).

Forsaken Power

20:43 Hanging the trophy at the Sacrificial Stones unlocks the Bonemass power, for years the community's clear favorite: five minutes of heavy resistance to all physical damage, enough to make most melee enemies, bosses and Fuling camps survivable. Like every power it lasts 300 seconds, shares one 20-minute cooldown with the others, and is also given to any player within 10 meters of the one who activates it (Valheim Wiki).

14:53 The Call to Arms Update of 2025 rebalanced all seven powers and trimmed this one. Since patch 0.221.3 (public test, Aug 20, 2025) and its live release 0.221.4 (Sep 9, 2025), the Bonemass power gives 25 percent resistance to pierce, slash and blunt damage instead of the previous 50 percent, and in exchange removes the stamina cost of blocking entirely and returns 5 stamina on every block (Game Rant; Game Rant, September 2025). Its resistance does not stack with the Crystal Heart trinket (Valheim Wiki). Commentators generally read the change as a mild nerf that kept the power among the strongest for shield users.

After the fight

7:49 Killing Bonemass changes the world. It unlocks the raid "A foul smell from the swamp", in which the boss's army of three Draugr and six skeletons attacks a base for 150 seconds under a rain that leaves the defenders wet, plus the "A skeleton surprise!" raid, and, until Moder is dead, "A cold wind blows from the mountains", where Drakes fly over walls and spit frost at players and livestock (Valheim Wiki). Skeletons also begin to spawn at night in the Meadows, Black Forest, Swamp, Mountain and Plains. See Raids and Events.

With the Wishbone in hand the intended route is uphill: silver, Wolf armor and the Mountain's boss Moder. Since 1.0 the Mountain also holds the Forge of Potential, whose Iron idols push the iron gear used against Bonemass past quality four.

Lore and name

The rune stone at the altar speaks of a tomb beneath the wanderer's feet and of a thousand bones without their flesh, and when Bonemass dies it thanks the warrior for releasing those who lived on in that shape, denied the peace of death (Valheim Wiki). The boss is the swamp's dead given a single body, which is why its summons are skeletons; the Steam achievement for the kill, one of the 53 added in 1.0, calls it the Writhing Dead (BisectHosting; games.gg). Two days after launch that achievement, titled simply "Bonemass", showed a global unlock rate of 0.1 percent on Steam, tracking having started fresh with 1.0. The wider mythology is covered under Lore and Setting.

48:27 Bonemass has its own boss theme in Patrik Jarlestam's score, a dirge of low drums and drones that plays for the length of the fight; see Soundtrack.

Status in 1.0

The 1.0 patch notes of Sep 9, 2026 list no change to Bonemass itself; its health, attacks, resistances, drops and power are as they were after Call to Arms (Beebom; Game8). What changed is the swamp around it, with the new Writhan creature and alternate biome generation at the edges of new worlds; see Deep North Update (1.0 Patch Notes) and Swamp Creatures.

Frequently asked questions

How do you summon Bonemass? Place ten Withered Bones on the giant skull altar in the Swamp. The bones come from the Muddy Scrap Piles inside Sunken Crypts and occasionally from swamp chests, so a player who has cleared enough crypts for an iron kit usually has them already.

What is Bonemass weak to? Blunt and frost, both at 1.5x. It takes half damage from slash, a quarter from fire and pierce, and is immune to poison, so a mace, an Iron Sledge or frost arrows beat swords, axes and ordinary arrows.

Where is the Bonemass altar? Somewhere in a Swamp, marked on the map by reading a Vegvisir beside a ruined Swamp Runestone Tower or inside a Sunken Crypt. A Vegvisir reveals only the altar nearest itself, so the skull it marks may lie in a different swamp.

What does Bonemass drop? Its trophy and one Wishbone for every player in the fight. The Wishbone detects buried silver veins in the Mountain, muddy scrap piles in the swamp and buried treasure in the Meadows.

What does the Bonemass Forsaken Power do? Since the Call to Arms Update it gives 25 percent resistance to pierce, slash and blunt damage for 300 seconds, removes the stamina cost of blocking and returns 5 stamina on every block. It shares a 20-minute cooldown with the other powers and does not stack with the Crystal Heart trinket.

Sources

• Bonemass, Valheim Wiki (weirdgloop)
• Bonemass Trophy, Valheim Wiki (weirdgloop)
• Wishbone, Valheim Wiki (weirdgloop)
• Withered bone, Valheim Wiki (weirdgloop)
• Nimble Anklet, Valheim Wiki (weirdgloop)
• Vegvisir, Valheim Wiki (weirdgloop)
• Forsaken Power, Valheim Wiki (weirdgloop)
• Bonemass, Valheim Wiki (Fandom)
• Valheim boss checklist, Physgun
• Valheim's Latest Update Adds a Brand-New Mechanic (Call to Arms patch notes), Game Rant
• Valheim Releases New Update for September 2025 (Patch 0.221.4), Game Rant
• Valheim 1.0 Achievements Guide, BisectHosting
• Valheim 1.0 Guide: All Achievements & How to Unlock Them, games.gg
• Valheim achievements, Steam Community
• Valheim 1.0 Patch Notes, Beebom
• Valheim 1.0 Patch Notes and Changes, Game8
• Press, Iron Gate Studio