The following material is Open Game Content from the Menace Manual SRD
Fiends appear in countless forms, although their physical characteristics often reflect some sin or other vile aspect.
Fiends share the following traits:
Darkvision (Ex): Fiends have darkvision out to a range of 60 feet. Darkvision is black and white only, but it is otherwise like normal sight, and a fiend can function with no light at all.
Allegiances: All fiends have a primary allegiance to evil. Fiends may also have an allegiance to either chaos or law.
Weapon and Armor Proficiency: Fiends receive either Archaic Weapons Proficiency or Simple Weapons Proficiency as a bonus feat. They are proficient with their natural weapons and any weapon mentioned in their entries. Fiends noted for wearing armor gain the bonus feat Armor Proficiency with whatever type of armor they are accustomed to wearing (light, medium, heavy), as well as all lighter types.
Languages: Fiends can speak Abyssal (the language of demons) and a number of additional languages equal to their Intelligence bonus. Fiends with an Intelligence of 8 or higher can also read and write these languages.
Special: Fiends cannot be raised from the dead.
Harriken (Headsnatcher Fiend)
A harriken can detach its head from its body and replace it with the decapitated head of any humanoid creature. In so doing, it can assume the dead creature’s form.
To kill a harriken, one must destroy its head. While wearing the head and assuming the form of another creature, a harriken will usually entrust its detached head to loyal underlings or hide it somewhere safe.
Attach Head (Ex): As an attack or move action, a harriken can attach a head (either its own detached head or the severed head of any Medium-size humanoid creature) to its headless body. It gains the visual, auditory, and olfactory senses of the creature whose head it wears; if the creature had low-light vision, for instance, the harriken gains this ability for as long as the head is worn.
The creature from which the head is taken must have died within the past 24 hours; otherwise, any attempt by the harriken to graft the head onto its body fails.
Body Blindsight (Ex): A harriken’s headless body can sense its surroundings as though it has the blindsight ability with a range of 30 feet. However, without its own head, the harriken loses its darkvision.
Detach Head (Ex): As an attack or move action, a harriken can detach the head (either its own head or the severed head of any Medium-size humanoid creature) from its body.
Disguise Self (Su): The harriken can assume the appearance of a specific Medium-size humanoid creature by attaching the creature’s severed head to its body. The illusion lasts as long as the head remains attached. The harriken does not gain any of the creature’s abilities, mannerisms, or knowledge, but it gains a +10 bonus on Disguise checks. Other creatures get a Will save (DC 10 + 1/2 the harriken’s Hit Dice + its Charisma modifier) to pierce the illusion if they interact with it (such as by touching the harriken and having that sensory input not match what they see). A true seeing spell reveals the harriken’s actual horrific appearance.
Electrical Rejuvenation (Ex): A harriken is immune to electricity. Furthermore, it heals 1 point of damage for every die of electricity damage it would take normally. For example, a 6d6 lightning bolt heals 6 points of damage to the harriken.
Fire Resistance 10 (Ex): A harriken ignores the first 10 points of damage from any attack that deals fire damage.
Indestructible Body (Su): While its head is attached to its body, a harriken can be killed. However, if its head is detached, the body stops taking damage when reduced to 1 hit point. Any damage dealt to the body that would knock it below 1 hit point is ignored. If the harriken’s detached head is found and destroyed (Defense 7; hp 5), the harriken’s body is instantly slain.
Telepathy (Su): A harriken can communicate telepathically with any creature within 100 feet that has a language.
Harriken (headsnatcher fiend): CR 4; Medium-size outsider; HD 4d8+4; hp 22; Mas 13; Init +0; Spd 30 ft.; Defense 21 (+9 natural, +2 leather armor), touch 10, flatfooted 21; BAB +4; Grap +5; Atk +5 melee (1d6+1, slam) or +5 melee (1d8+1/19–20, longsword); Full Atk +5 melee (1d6+1, slam) or +5 melee (1d8+1/19–20, longsword) or +4 ranged; FS 5 ft. by 5 ft.; Reach 5 ft.; SQ Attach head, body blindsight, darkvision 60 ft., detach head, disguise self (DC 15), electrical rejuvenation, fire resistance 10, indestructible body, telepathy; AL evil; SV Fort +5, Ref +4, Will +6; AP 0; Rep +0; Str 13, Dex 11, Con 13, Int 16, Wis 15, Cha 16.
Skills: Bluff +10, Disguise +10 (+20 when using disguise self ability), Hide +6, Intimidate +9, Listen +6, Move Silently +6, Read/Write Abyssal, Read/Write Languages (any three), Sense Motive +6, Speak Abyssal, Speak Languages (any three), Spot +6.
Feat: Heroic Surge (1/day).
Advancement: By character class.