Well, this is what we have here, Ardat, Demon Queen of Harpies.
I built her abilities up from a normal harpy with elite array ability scores, then ability increase for increased sized and Hit Dice/levels. Then the demon lord and multi-headed templats, and gave her inherent bonuses on three of her ability scores (Dex, Int, and Cha).
I retain most of her rogue abilities except for trapfinding. I also gave her fast heal and summon harpies.
Ardat the Unavowed CR 25
Demon Queen of Harpies
Always CE Large Outsider (chaotic, evil, extraplanar, tanar’ri)
Initiative: +12 (+8 dex, +4 improved initiative)
Senses: Darkvision 60 ft’ Listen +30, Spot +26
Languages: Abyssal, Common, Telepathy 300 ft
Armor Class: 44 (-1 size, +16 natural, +8 dex, +10 deflection, +3 insight)
Flat footed 44 (Improved uncanny dodge)
Touch 38
Hit Dice: 31 (388 hp); Fast heal 8
Immune Electricity, mind-affecting effects, poison, sonic
Resist Acid 10, cold 10, fire 10; SR 28
Fort +38 Ref +25; improved evasion Will +22
Speed 30 ft (6 squares), fly 40 ft (average)
Melee 2 large +6 chaotic unholy longswords +46/+41/+36/+31
(2d8+15 plus 2d6 chaotic & 2d6 uholy)
2 claws +37 (1d6+4)
2 wing slams +37 (1d8+4)
Space/Reach: 10 ft/10 ft
Base Atk +31; Grp +44
Atk Options Flyby attack, power attack, sneak attack +10d6, wingstorm
Special Actions Captivating song, shriek, summon harpies, summon tanar’ri,
Sunder enchantment
Spell-like abilities – CL 22nd
At will: astral projection, blasphemy, confusion, desecrate, detect good, detect law, greater dispel magic, greater teleport, plane shift, shapechange, suggestion, telekinesis, unhallow, unholy aura, unholy blight
2/day – antipathy, demand
1/day – any symbol, dominate monster, powerword kill
Abilities: Str28, Dex26, Con27 Int18 Wis16 Cha30
SA: Captivating song, shriek, sneak attack +10d6, summon harpies, summon tanr’ri
SQ: Improved evasion, improved uncanny dodge, outsider traits, sunder enchantment,
Superior two-weapon fighting, tanar’ri traits
Feats: Ability focus (Captivating song)(B), Dark Speech, Dodge, Flyby Attack, Hover,
Improved Initiative (B), Combat Reflexes (B), Iron Will, Multiattack, Persuasive,
Skill Focus (oratory)(B), Weapon Focus (Claws)(B), Weapon Focus (Longsword)
Wingstorm
Skills: Balance +29, Bluff +50, Climb+26, Concentration +42, Diplomacy +52,
Escape Artist +25, Gather Information +31, Hide +21, Intimidate +50, Jump +30,
Knowledge (Local) +21, Listen +30, Move Silently +42, Perform (Oratory) +47,
Search +31, Sense Motive +37, Spot +26, Tumble +46, Use Magic Device +44
Possessions: 2 large +6 Chaotic Unholy Longswords
Captivating Song (Su): When Ardat sings, all creatures in a 300 foot spread must succeed a DC 37 Will save or become captivated. This is a sonic, mind-affecting effect. A creature who made the save is immune to Ardat’s song for 24 hours. The save DC is Charisma-based.
A captivated victim walks toward the Harpy Queen, taking the most direct route possible. If the path leads to a dangerous area (through flame, a cliff, or the like), the victim gets a second saving throw. Captivated victims can take no actions but to defend themselves. A victim within 5 feet of Ardat stands there and offers no resistance to her attacks. This effect continues for as long as Ardat sings and for 1 round thereafter. A bard’s countersong ability allows the captivated creature to attempt a new will save.
Shriek (Su): Each of Ardat’s three heads can unleash a blood chilling shriek as a move action. Once a head shrieks, it may not do so for 1d4 rounds. All three heads can shriek simultaneously as a full around action. Each shriek affects all creatures in a 60-foot radius spread. Ardat’s left headed shriek deals 1d6 points of Int drain, the right head deals 1d6 Wis drain, and the central head deals 1d6 Cha drain. A successful Will Save DC35 negates the ability drain but leaves the target shaken for 1d4 rounds nevertheless. A creature that would normally be drained to 0 points in any ability score by this attack instead left at a score of 1 and is driven permanently insane, such that he sees his allies as his enemies and does everything in his power to murder said allies. This insanity can be cured by greater restoration, miracle, or wish. This is a sonic, mind-affecting effect. The save DC is Charisma-based.
Sneak Attack (Ex): Whenever Ardat successfully attacked an opponent who is denied its dexterity bonus, she does an additional 10d6 damage. This however, do not affect creatures that are immune to critical hits (undead, constructs, etc).
Summon Harpies (Sp): Once per day Ardat automatically summons 2d4+4 harpies, or alternatively, 1d4 Soul Sirens (Half fiend harpy 6Bard/6 Ranger). This is equivalent to a 9th level spell.
Summon Tanar’ri (Sp): Once per day Ardat can automatically summon 1d6 succubi or 1d4 vrocks. This is equivalent to a 9th level spell.
Improved Evasion (Ex): The Harpy Queen takes half damage even if she failed a Reflex save. She loses this benefit if she is immobilized.
Improved Uncanny dodge (Ex): Ardat retains her dexterity bonus even if she is caught flat-footed or struck by an invisible attacker. She cannot be flanked. She cannot be sneak attacked unless the attacked is at least 24th level. She is denied this benefit if she is immobilized.
Sunder Enchantment (Su): Ardat’s touch functions as a break enchantment spell (CL 20th), sundering enchantments, transmutations, and curses. If the creature that placed the above effect that is broken is within 30 feet of Ardat when she sunders that creature’s effect, that creature takes 20d6 points of nonlethal damage and is stunned for 1d4 rounds as the backlash of its own magic strikes it. A successful Fort DC 35 save halves this nonlethal damage and negates the stunning. The save DC is Charisma-based.
Superior Two-Weapons Fighting (Ex): Because of her two additional heads, both of Ardat’s hands function as primary hands when wielding a weapon, thus she suffers no penalties when attacking with two weapons.
Skills: Ardat has the following racial bonuses to the following skills: a+10 to Listen checks, +6 bonus to Search & Spot checks, and +4 to bluff checks.