Buy RS3 Skull piece
The Skull piece is a members-only item in RuneScape 3. It is a rare drop from Wallasalkis, which live underneath Waterbirth Island. The item is tradeable, and its examine text calls it "a fearsome looking skull."
The Skull piece is a key part of making skeletal armour. You can trade it to Peer the Seer, along with dagannoth hides and coins, to get a skeletal helm. If you also bring a fibula piece, a ribcage piece, 6 dagannoth hides, and 22,500 coins, Peer the Seer will give you full skeletal armour.
The Skull piece has another use too. It works with the Tune Banite Ore spell to tune banite ores into wallasalkibanite ores. This makes it useful for players who work with banite metal.
You cannot buy a Skull piece from any store in the game. Hunting Wallasalkis for one takes time, since the drop is rare. Getting a Skull piece here saves you long trips under Waterbirth Island and gets you closer to a full set of skeletal armour.