Undead fire giant skeleton filled with dangerous, constantly-aflame fluids

Although rare, Lava Lake Skeletons have been immortalized due to how dangerous and resilient they are. They are created through a special ritual that involves the corpse of a fire giant, an active volcano, and a large, expensive ruby. The ruby is placed within the mouth of the corpse and then the prepared body is thrown into a volcano. After three days of ritualistic chanting, the necromancer is able to raise said creature from the dead, now filled with dangerous, constantly-aflame fluids. Unlike their living counterparts, lava lake skeletons do not need to find a rock to throw. Instead, they manifest said lava-filled rock within their appendages to throw at their opponents. The damage dealt by this attack counts as fire damage. Just like normal skeletons, lava lake skeletons take only half-damage from edged weapons, and only a single point from arrows, bolts, or sling stones (plus any magical bonus). As with all undead, they can be Turned by Clerics as a spectre, and are immune to sleep, charm, or hold magic. As they are mindless, no form of mind reading is of any use against them. Lava lake skeletons never fail morale, and thus always fight until destroyed.