Mangled bones are obtained when fighting the monsters or rummaging the barbarian skeletons found on the ground within the Ancient Cavern. With any type of logs, a hatchet, and a tinderbox, players can use it on the burnt space (pyre site) to make a pyre ship.
A sure way of getting mangled bones is by killing confused barbarians or lost barbarians, as they always drop them.
Note: if rummaging a skeleton at least 2 slots must be free because of the random chance of finding an ancient page for my notes. If you do not have enough slots free, the bones will "disintegrate".
Mangled bones also do not give the Prayer experience bonus that chewed bones give.
If the bones are lost on death, when returning to claim items from the grave, they will have become normal bones.
When burned in a barbarian funeral boat during the Barbarian Training will release a ferocious barbarian spirit, which after killing will drop a reward at its feet. However, players cannot receive a dragon full helmet, which can only be obtained from chewed bone pyre ships or as a drop from mithril dragons.
A player burning mangled bones, summoning a ferocious barbarian spirit
For an exhaustive list of all known sources for this item, see here
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