The Obsidian Skull is a wearable item that grants the wearer immunity to damage from fire-based blocks, such as Meteorite, Hellstone, and Hellstone Bricks. It also gives an additional one point of Defense when placed in an accessory slot. The skull cannot be worn in the head slot. It can only be obtained by crafting it with 20 Obsidian at any Furnace.
The Obsidian Skull can be combined with the Cobalt Shield to create an Obsidian Shield, for a combined effect of knockback immunity, fire block damage immunity, and a 2-point defense bonus. The Obsidian Skull can also be combined with the Lucky Horseshoe to create an Obsidian Horseshoe, for a combined effect of fall damage immunity and fire block damage immunity. Both accessories must be crafted at the Tinkerer's Workshop.
They can be sold for a respectable amount of money easily, due to the minority of resources needed to craft them.