When a particularly powerful demon perishes, its soul might persist for a time as a cacodemon. Like souls that walk the Shadowfell waiting for their final fate, a cacodemon exists for a length of time proportional to the demon’s power in life. Unlike a Shadowfell soul, a cacodemon can end its wandering by possessing a body or an object.
Although a cacodemon is a demon’s life force, it behaves as a hazard or a trap rather than as a monster. In today's Demonomicon excerpt, we see just how.
Possessing Soulless Bodies
A cacodemon’s easiest prospects for possession are soulless bodies, plentiful in the Abyss. Soulless demons are the most common type of demon, and powerful examples of such creatures become fodder for greater fiends.
The risk involved in possessing a soulless body—particularly a nondemon body—is that while the cacodemon animus retains its personality and experiences, it is only as physically powerful as the body it possesses. Unlike possessing an object (see below), once a cacodemon possesses a soulless body, it is bound within it until that body is destroyed. Moreover, if a demon possessing a body is slain, it has no guarantee that its animus will become a cacodemon again.
Objects and Constructs
Cacodemons can also possess magic objects or constructs, though they typically need to be coerced into possessing the latter. As with standard possession, the demon can see and hear through the object. However, without some mechanical form of locomotion, the demonic object cannot move without a considerable expenditure of will. A cacodemon might possess a magic object in hopes of later possessing the object’s carrier or guardian. In this way, the cacodemon gains mobility while waiting for a more suitable host.
Possessing a construct comes with the same perils as possessing a soulless body. As a result, few cacodemons willingly possess a construct. Powerful demons and demonologists sometimes create demon-possessed constructs by tricking or compelling cacodemons into construct bodies. The demon lord Haagenti is a notorious purveyor of demonic constructs, including clockwork horrors (Demonomicon, p.109).
Hosts with Souls
More often than not, the intended victim of cacodemon possession senses the intrusion and fights to stave off the attack. As a result, a cacodemon chooses a victim weaker than itself whenever possible. If a cacodemon attempts such a possession and fails, it risks redirection into a magic object, entrapment in a magic circle, or depletion to the point that it can no longer possess a vessel and fades to nothingness. As with possession of a soulless body, the cacodemon also might not manifest again as a cacodemon if its host dies.
This type of possession offers the opportunity to gain power quickly. Motivated mortals can achieve nearly godlike power in decades or years, whereas passing through even the lowest ranks of standard demonic ascension can take centuries. Moreover, as the cacodemon cultivates and slowly devours the soul of its host, it gains as much power in the process as it would gain by consuming impossibly vast quantities of soul larvae.
When no vestige remains of a possessed body’s original soul, the Abyss sometimes transforms animus and body into a true demon. Sages and demonologists believe that the frost giant Kostchtchie (Demonomicon, p.122) became a demon lord through cacodemon possession.
XP by previous form
A cacodemon can attempt to possess any creature within the area it haunts.
Additional Skill: Arcana (trained only)
Additional Skills: Arcana, Religion
Moderate DC by level, after the cacodemon attacks or takes on its mist form: The character identifies the cacodemon. Initiative
equal to that of the cacodemon’s previous form
The cacodemon rolls initiative and attacks when any creature enters its haunted area.
Standard Action Melee
Target: One creature in haunted area
Attack: Level of cacodemon’s previous form + 3 vs. Will
Hit: The target is dominated (save ends). First Failed Saving Throw: The target is still dominated, but it is no longer dazed as part of that condition. The cacodemon chooses all the dominated target’s actions. Second Failed Saving Throw: The cacodemon possesses the target (see "Demon-Possessed," p.12). The possession ends when the target dies or the cacodemon is exorcised (see "Countermeasures" below).
Miss: The cacodemon manifests as a misty essence in a square adjacent to the target. While in this form, the cacodemon can attack only creatures adjacent to it or in its square. Any creature can move through the cacodemon’s square freely. The cacodemon cannot move or be attacked or damaged. The hazard makes a saving throw at the end of each of its turns. On a save, this effect ends.
Friday: Although individual demons of the same type resemble each other, this chaotic nature can manifest in differences between them. Likewise, creatures tainted by demonic power can adopt a dizzying array of new abilities and twisted forms.