Buy RS3 Wyrm heart
The wyrm heart is a rare drop in RuneScape 3. It comes from lava strykewyrms in the Wilderness. The boss version, the WildyWyrm, can also drop it. Its examine text says it is still beating even after death.
The heart has one main use. Attach it to a staff of light to make the staff of darkness. The new staff starts with 50% charges. The staff of darkness degrades as you fight with it. You can recharge it by 50% with another staff of light. After 10 hours of combat, the staff of light part is used up. You keep the wyrm heart. You can also undo the staff, but only the heart is saved.
The wyrm heart is a members-only item. It is tradeable and noteable, so it is easy to move and trade. It weighs 0.453 kg. It can be disassembled, which almost always gives Simple parts and rarely gives Variable components. Most of the result is junk.
This item is a good pick for mages who want the staff of darkness or for players who want to keep spare hearts to recharge one.