Possessed Creature
A possessed creature is any corporeal creature that is being controlled by another entity that is located, both physically and mentally, inside the original corporeal creature. This occurs most often when an outsider or incorporeal undead manages to enter the body through an insubstantial state and the corporeal creature fails its attempt to resist being overridden. The result is a creature that looks, smells, sounds and feels like the original creature, but does not move, talk or act like the original creature. For those fortunate enough to study the phenomena, it is clear the the invading entity does not always have perfect control over the new body, particularly when the issue of distance, speed, balance or strength becomes a concern.
Even with this 'training-wheel' handicap, possessed creatures are quite dangerous to deal with. In addition to having many of the physical aspects of the host and the mental and mystical capabilities of the invader, often there are few ways to deal with the problem without killing the host, which only causes the invader to be forced from the body. In a situation where adventurers are not prepared for it, an otherwise honest and noble NPC might suddenly attack the party and the party would easily kill the poor man, letting the invading devil time to escape and possess a member of the city guard, all the while framing the party for a string of suicide-by-adventurer. Examples of Possessed Creatures include:
Creating a Possessed Creature.
To determine the statistics of a possessed creature, you must first determine the host creature and the invading creature (referred to hereafter as the host and invader). The host must be a corporeal creature that has been possessed as per the Possession rules. The invader must be a creature capable of possession, usually an outsider or incorporeal undead. It is important to remember that a Possessed Creature can only maintain this mode of possession for a short period of time, usually a number of minutes equal to 1/2 the invader's Hit Dice + the invader's Charisma modifier + 1 for every time the invader has successfully assumed the Controller mode so far, although hosts that are willingly possessed can allow the invader to maintain this mode for an equal number of hours.
CR: If the host is not primarily combative. such as a non-heroic NPC, or a primarily a spellcaster that is not willing to be possessed, the CR of the possessed creature is equal to the invader's normal CR +1. If the host is primarily combative, or is primarily a spellcaster that is willing to be possessed, the CR of the possessed creature is equal to the higher CR of either the host or the invader, with an additional +2.
Alignment: As per the invader. Also, the aura of the invader's alignment is still the same, as per the Detect Evil or similar spell.
Size and Type: As per the host.
AC: The armor class of a possessed creature is determined normally, using the following modifiers from both the host and the invader.
Hit Dice: As per the host. It is important to remember that any hit point damage done to the possessed creature is done to the host, thus even after a possession ends, the host will still be injured from any wounds sustained while possessed. Should this be enough to kill the possessed creature, only the host dies, while the invader is free to depart, although it is common for the invader to immediately manifest, given the lack of suitable host.
Defensive Abilities: Certain defensive abilities of the possessed creature come from both the host and the invader. While some of the more common ones are detailed below, if the defensive ability is based on the host's body, without the need to specifically choose to activate it, it is kept, using the host's original aspects. If the defensive ability needs to be chosen to be activated, it is only kept if it comes solely from the mind of invader or is one that both the host and the invader share.
Speed: As per the host, including all movement rates of the host.
Initiative: The possessed creature retains the host's Dexterity bonus to initiative, but any other modifiers, such as feats, must come from the invader.
Attacks: Any natural attacks and special effects of those natural attacks (grab, trip, poison, etc) are from the host. Any weapon proficiencies are from the invader, although if the host does not have the ability to wield weapons, then neither does the possessed creature it is based on. The BAB used is the highest of either the host or the invader.
Damage: Damage from any natural attack is determined from the host. Any weapons that the possessed creature might used must be sized appropriately for the host.
Space / Reach: As per the host.
Special Attacks: Any extraordinary special attack based on Strength, Dexterity or Constitution that the host has is kept. Any supernatural special attack based on Intelligence, Wisdom or Charisma that the invader has is also kept.
Abilities: To determine the attributes of a Possessed Creature, use the host's Strength, Dexterity and Constitution and invader's Intelligence, Wisdom and Charisma. If the host does not have one of the physical attributes, or if the invader does not have one the mental attributes, then neither does the Possessed creature.
Feats: To determine the feats of a possessed creature, first, list the feats for both the host and invader. Keep any feats that appear on both lists. This becomes the first group of feats for the possessed creature.
Next, of those that remain on the host's list, remove any feat that requires a conscious effort to use. This includes any feat that must be chosen at the beginning of the combat round, like Combat Expertise, Deadly Aim and Power Attack, any feat that allows the host to do something new, like any Metamagic or Item Creation feat, any feat that provides a bonus to Will saves and any feat that requires or augments a class-specific ability. Finally, remove any feat that remains that the prerequisites are no longer met.
Likewise, of the feats remaining on the invader's list, remove any feat that relies on the invader's body and any feat that the prerequisites are no longer meat. This would include feats like Ability Focus (for abilities based on the invader's own physical form), Combat Reflexes (unless the host had the Dexterity 13 prerequisite) and Improved Natural Armor. Those that remain from both lists are added to the original group of feats that appeared on both feats and these become the feats for possessed creature.
This might easily provide the possessed creature with more feats that what its' Hit Dice would allow. Treat these feats as bonus feats. Examples of host feats that would remain include Endurance, Great Fortitude, Improved Natural Armor, Improved Natural Attack, Lightning Reflexes, Run and Skill Focus, while feats kept from the invader would include Combat Expertise, Iron Will, Skill Focus and Weapon Focus. The possessed creature is assumed to have whatever armor, shield and weapon proficiencies that both host and the invader have.
Skills: The number of ranks a possessed creature has is the highest of either the host or the invader, determined individually by skill. The attribute modifiers for these skills are determined normally, using the possessed creature's attributes as detailed above. Any unusual alteration to a skill's normal use can only come from the invader. Thus, a rogue host may have the Fast Picks or Fast Stealth rogue talents, but the invading ghost cannot make use them. A possessed creature knows all of the languages of both host and invader.
Special Qualities: Taking into account the special defenses already listed above, the vast majority of remaining special qualities that a possessed creature could have come from the invader. The only special qualities that are retained from the host are any senses (except telepathy) and any extraordinary abilities that do not need to be activated or are based on a physical attribute (Strength, Dexterity or Constitution). The invader retains any extraordinary or supernatural abilities that rely on Intelligence, Wisdom or Charisma, as well as any spell-like abilities. If the invader has spellcasting capabilities, these are also kept, but are only useful if the host if physically capable of casting spells (meaning talking and has at least one hand-like appendage).
A special note concerning the spell-like abilities and spellcasting capabilities of host should be mentioned. If the host is willing to be possessed, both at the time the possessed started and at the time when the invader wishes to call upon on the mystical abilities of the host, the possessed creature can use a spell-like ability or cast a spell from the host as its action. Doing this requires the host, not the invader, to make a concentration check, DC 15 + spell level, to even attempt the spell. This concentration check is in addition to and separate from any additional concentration checks needed, such as casting while threatened. If psionic rules are used, then the same mechanic holds true for them as well.
Special Disadvantages: Any vulnerabilities to specific energy types that the host has are retained by the possessed creature. Any effect based on alignment or aura is determined by the invader. However, any effects that are affected by creature type or sub-type are determined by both (using the one most detrimental to the invader). Also, all possessed creatures are vulnerable to having the invader forced from the host's body without the host being damaged in the process. See the Possession rules for details, but most notably, a Dispel Evil or appropriately similar spell can drive out an invader with a successful caster check with a DC equal to 10 + the invader's Hit Dice + the invader's Charisma modifier. Likewise, Banishment and Dismissal also drive out an invader that fails its saving throw.
Environment: As per the host.
Organization: As per the invader, although usually this is solitary.
Treasure: As per the host, although an invader may arrange for key equipment to be retrieved after a successful possession.
Source: ECB, pg. 290