A smouldering stone is a stone dropped by Cerberus and much more rarely, hellhounds. It can be used to upgrade the dragon axe, dragon harpoon, and dragon pickaxe into the infernal axe, infernal harpoon, and infernal pickaxe, respectively. These infernal tools have 5,000 charges and once fully depleted, another stone or corresponding dragon tool must be used to recharge it.
Boosts cannot be used to use the smouldering stone to create any of the infernal tools; the player must have the required base levels of either 85 Firemaking for the infernal axe, 85 Smithing for the infernal pickaxe, or 85 Cooking for the infernal harpoon.
The stone can be dropped by hellhounds as well, although at a much rarer rate. When dropped by a hellhound, a message will appear in the player’s chatbox: “Something hot drops from the body of your vanquished foe.”