Bonemass
The Swamp boss, a hulking mass of bone and ooze that resists everything except blunt damage and drops the Wishbone.
Bonemass is the third Forsaken and the classic difficulty wall. It is a hulking mass of bone and ooze that shrugs off most weapons and poisons you while you fight it. The trick is not damage, it is preparation: bring the right weapon, the right mead, and a clear head. Win and you get the Wishbone, which finds silver and treasure for the rest of the run.
Where and when
Bonemass lives in the Swamp, the third biome, where you also gather iron. You fight it after the Elder, once you have iron gear and poison resist mead brewed. Summon it at its altar in the Swamp.
How to summon
Offer 10 Withered Bones at Bonemass’s altar. Withered Bones come from Sunken Crypts and from the muddy piles around the Swamp. Stockpile ten while you are mining iron, then bring them to the altar.
How to fight it
Bonemass resists Slash, Pierce, and Fire, so leave the sword and bow at home. It takes full damage only from Blunt, which means an iron Mace, and it is weak to Poison-cleansing tactics, so the Poison Forsaken Power and frost arrows help chip it. Drink poison resist mead before and during the fight, because its poison cloud is constant and will kill you without it. Stand in close, swing the mace, and keep re-drinking mead as it wears off. The fight is a slog by design, so keep your stamina up and your feet on solid ground.
Do not enter the Swamp, let alone this fight, without poison resist mead and a Mace. Slash and pierce weapons barely scratch Bonemass, and unmitigated poison will outpace your healing.
Drops and Forsaken Power
Bonemass drops the Wishbone, which pings nearby buried silver and treasure. It is progression-critical: without it you cannot reliably find the silver veins under the Mountains. It also drops the Bonemass trophy. Hang the trophy on the Sacrificial Stones to activate its Forsaken Power: a 50 percent boost to physical resistance against blunt, slash, and pierce, the strongest defensive power in the game.
Next: Moder in the Mountains. For the whole run on one page, see the full-run progression cheatsheet.