I dont' have the FC handy, but here's some relevant bits from BoVD:
A fiend can possess an object of at least Tiny size and no larger than Huge. An item held, worn, or carried by a character (including magic items) uses its owner's saving throw to resist possession. Unattended magic items gain a saving throw as if a spell was being cast upon the item. In each case, the Will save DC is 10 + 1/2 the fiend's HD + the fiend's Charisma modifier. A fiend with the possession ability automatically succeeds when attempting to possess an unattended, nonmagical item.
A fiend possessing an object becomes a part of the object. A possessing fiend can see and hear up to 60 feet away from the object, but it can't use darkvision or blindsight while possessing an object, even if it ordinarily has these abilities. The possessing fiend remains vulnerable to spells that affect outsiders, extraplanar creatures, or evil creatures (such as holy word and holy smite) and mind-affecting spells and effects. Physical attacks and most spells (such as fireball) don't affect the fiend, but they might affect the object. Harming the object does not harm the possessing fiend; if the object is destroyed, the fiend takes ethereal form and can choose a new host object (or creature).
A fiend can also possess a substance that has no fixed shape (such as a pool of water or a dust cloud) or is part of a larger object (such as a section of a wall). When it does so, a fiend cannot possess an area or a volume larger than 10 feet on a side.
A fiend possessing an object can take any of the following roles. Changing roles is a standard action.
Controller: If the possessed object has moving parts, such as a wagon, clock, or crossbow, a possessing fiend can control the movement. A wagon can be made to steer toward a pedestrian on a street or roll out of a stable with no horse pulling it. A clock can slow or run backward. A crossbow can




and fire (but not aim or load itself). Possessed objects with wheels or legs cannot move faster than the fiend itself could move in its corporeal form.
More powerful fiends can exert greater control. A fiend with at least 10 HD and Charisma 17 can force an object to animate even if the object doesn't have any moving parts (such as a table or statue). The possessed object functions as an animated object (see the Monster Manual). However, no fiend can control an animated object with a higher Challenge Rating than the fiend's.
Enhancer: A fiend can possess a Tiny or larger weapon or armor and enhance it as if it were a magic item. The fiend can duplicate magic item powers worth up to 2,000 gp per Hit Die. For example, a hezrou (9 HD) that enhances a longsword could bestow up to 18,000 gp worth of powers on it. It could duplicate the effect of a +3 longsword, a +1 unholy longsword, or another combination. A fiend that possesses magic armor or a magic weapon can increase its power by the same amount. Table 8-3: Armors and Table 8-10: Weapons in the DMG give prices for various enhancements.
The fiend is in control of the powers it bestows upon the item. It can take them away as a free action at a moment's notice if the creature using the item does not act in a manner that the fiend wishes. If the fiend leaves the items, it loses all powers bestowed by the possession.
Despite the fiend's duplication of magic item abilities, a nonmagical possessed item doesn't become actually magical. Detect magic will not sense an aura; detect evil will, however. Smart characters might notice that the possessed item behaves strangely or has an unusual appearance (a magic weapon that isn't masterwork quality, for example, is a tipoff that something is awry). A character who succeeds at a Search check (DC 25) notes that there is "something strange" about the item.