|Image by zerogenius.|
(Inspired by the Skull gang from City of Heroes. Man, I miss that game...)
In the first wars fought between the earliest human kingdoms, warrior-cults grew up which practised various forms of ritual cannibalism in order to absorb the life-force of their enemies. Some ate the flesh of the vanquished; some drank their blood, and some made talismans from their bones. Through years of gruesome trial and error, a fairly reliable methodology for stealing the power of the dead was developed. First, one must kill an adult human, eat their heart, and drink their heart's blood; this conveys their strength to their killer, albeit briefly. Then, as soon as possible after doing this, one must cleanse the flesh from some of their bones and attach them to one's body, either by wearing them as clothing or by actually sewing or nailing them to one's flesh; this will hold the stolen life-force in. The most magically efficient bone to take is the face of the skull, and thus the practitioners of this horrible rite are generally known as Skull-Wearers, for they either wear the skulls of their victims as masks, or else stitch their skulls to their own faces; but other variants are possible, although a much greater quantity of bone is required if something other than the skull is used. Regardless of the variant, if the bones ever cease to be in contact with the flesh, the stolen life-force is lost, and the entire ritual must be repeated.
Today, skull-wearing is practised by a few isolated cannibal bands, and a few particularly brutal warlords insist that the warriors who serve them must prove themselves by undergoing the rite. (In the long term this is a terrible idea, as the warriors who perform the rite soon become so hateful and vicious as to be totally untrustworthy, but in the short term they make great shock troops.) In most lands, however, the practise is regarded with utter abhorrence, and those found to have performed it are ritually burned in order to remove the spiritual stain of them from the land.
Behind The Mask: Performing the Skull-Wearer rite immediately raises the ritualist's Strength and Constitution to 16, or to 18 if that stat was already 16 or higher. (For NPCs, give them a +2 bonus on to-hit and damage rolls in melee, and +2 HP per hit dice.) In the first hours after donning their skull, the ritualist feels fearless and invincible; but over the days that follow, they slide further and further into a black emotional morass, unable to feel anything except hate, resentment, pain, and rage. This makes them very difficult to get along with, and often leads them to make very bad decisions, as they assume that everything is always out to get them and that the appropriate way to respond is always with vindictive and disproportionate violence. Their Wisdom and Charisma each drop by 1 point per week until they reach 5; after this they drop by one per year until they reach 1, by which point the skull-wearer is little more than a murderous cannibal beast. Remember, however, that no matter how long they wear the skull, they retain their full normal Intelligence score.
Removing the skull causes immediate loss of the Strength and Constitution increases, which may cause instant death if the skull-wearer was relying on their extra HP to keep them alive; it also causes massive emotional trauma, as the ritualist's old personality comes flooding back and they suddenly have to cope with everything they've done since donning the skull. The ex-skull wearer will regain one point each of Wisdom and Charisma per day until they each return to their old score minus 1; the loss of this last point in each is permanent. Most ex-skull-wearers spend these days rocking back and forth, weeping uncontrollably. In extreme cases, they may carry on doing this for the rest of their lives.
Skull-wearers potentially present their enemies with a moral dilemma: if they are subdued, there could be a perfectly salvageable human being in there, under the mask. Admittedly, no matter who they were before, these are people who at some point killed and ate another human being; but what if they were forced into it, or have been led to re-evaluate their life choices by their time as a skull-wearing ghoul? Of course, the easy option is just to kill them all and let the gods sort it out, but capturing them and ripping their masks off instead could be an easy way to get some grateful new allies. Then again, it could also be an easy way of trapping yourself in the company of a manipulative psychopath who will gush on and on about how glad he is to be free of that horrible skull, all while planning which of you would make the best 'donor' for his new mask...