The infamous Choker spellcaster; also uses advanced HD to get stat points for Intelligence and to reduce the CR increase from spellcaster levels (technically it should only be CR 13 but I've bumped it up to CR 15 to provide some tenuous pretence of balance). I used wizard levels as the challenge appealed to me the most (plus it makes for a Choker that isn't outrageously powerful).

WARPED ONE (Advanced Choker Wizard 15th)

Hit Dice: 12d8+15d4+108 (199 hp)
Initiative: +7
Speed: 20 ft. (4 squares), climb 10 ft.
Armor Class: 23 (+3 Dex, +4 natural, +6 enchanted), touch 13, flat-footed 20
Base Attack/Grapple: +17/+26
Attack: Tentacle +28 melee (1d4+11)
Full Attack: 2 tentacles +28 melee (1d4+11)
Space/Reach: 5 ft./15 ft.
Special Attacks: Constrict 1d4+11, improved grab, spells
Special Qualities: Darkvision 60 ft., quickness, summon familiar
Saves: Fort +15, Ref +14, Will +17
Abilities: Str 20, Dex 16, Con 18, Int 18, Wis 14, Cha 4
Skills: Climb +13, Concentration +34, Hide +33, Knowledge (arcana, dungeoneering) +23, Listen +4, Move Silently +33, Spellcraft +29, Spot +4, Survival +2 (+4 underground), Use Magic Device -1 (+1 scrolls)
Feats: Alertness*, Enchanted, Great Fortitude, Greater MultigrabSK, Improved Familiar, Improved InitiativeB, Lightning Reflexes, Magical Aptitude, MultigrabSK, Practiced Spellcaster (wizard)CD, Reflexive Constriction, Scribe ScrollB
Environment: Underground
Organization: Solitary (plus homunculus familiar)
Challenge Rating: 15
Treasure: 1/10 coins; 50% goods; 50% items (plus headband of intellect +4)
Alignment: Usually chaotic evil
Advancement: By character class
Level Adjustment: -
*While familiar is within Warped One's reach (15 feet)
SKSerpent Kingdoms
CDComplete Divine

This alien creature lurks in the shadows above you, silently watching. You notice its long, sinuous arms coiling and writhing in the darkness. Suddenly,the creature attacks with supernatural speed, showering spells down upon your party and launching itself downwards to attack. Simultaneously, a ravenous imp darts into the fray with a venomous bite.

Warped Ones are the most devious of the already devious Choker race. They employ their racial speed to great effect, churning out spells far quicker than mortal spellcasters are capable. However, they are dependent on inherited or crafted headbands of intellect to make full use of their spells.

Chokers speak Abyssal, Common, Infernal, Terran, and Undercommon.

A Warped One haunts and stalks adventurers, unsettling them with its spells while remaining out of sight. When it finally deigns to enter combat it makes great use of its quickness ability, casting multiple protective spells upon itself and then dividing its actions between spells and physical attacks in subsequent rounds.

Due to its Multigrab, Greater Multigrab, and Reflexive Constriction feats, a Warped One is happy to constrict up to two foes and still continue spellcasting. Their homunculus familiars are relatively combat-ready, so a Warped One orders its familiar to attack alongside it.

Due to its Enchanted feat, a Warped One's natural weapons and any weapons it wields have a +6 enhancement bonus.

Constrict (Ex)
A Warped One deals 1d4+11 points of damage with a successful grapple check against a Huge or smaller creature. Because it seizes its victim by the neck, a creature in the Warped Ones grasp cannot speak or cast spells with verbal components.

Improved Grab (Ex)
To use this ability, a Warped One must hit a Huge or smaller opponent with a tentacle attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and can constrict. Warped Ones receive a +4 racial bonus on grapple checks, which is already included in the statistics block.

Quickness (Su)
Although not particularly dexterous, a Warped One is supernaturally quick. It can take an extra standard action or move action during its turn each round.

Summon Familiar
A Warped One is served by an advanced (6HD) homunculus familiar (see below).

A Warped One casts spells as a 19th-level wizard (including the benefits of its Practiced Spellcaster feat).

Typical Wizard Spells Prepared (spells per day: 4/5/5/5/5/4/3/2/1, save DC 14 + spell level)
0th: detect magic, ghost sound, message, mage hand; 1st-expeditious retreat, mage armour, magic missile (2), shield; 2nd: glitterdust, resist energy, scorching ray (2), see invisibility; 3rd: fly, protection from energy, stinking cloud, suggestion (2); 4th: black tentacles, fire shield (2), greater invisibility, stoneskin; 5th: baleful polymorph, cloudkill, cone of cold, feeblemind; 6th: antimagic field, chain lightning, greater heroism; 7th: mage's sword, spell turning; 8th: polar ray.

A Warped One has a +8 racial bonus on Climb checks and can always choose to take 10 on Climb checks, even if rushed or threatened.

Hit Dice: 6d10 (99 hp)
Initiative: +7
Speed: 20 ft. (4 squares), fly 50 ft. (good)
Armor Class: 23 (+3 Dex, +2 size, +8 natural), touch 15, flat-footed 20
Base Attack/Grapple: +4/-5
Attack: Bite +22 melee (1d4-1 plus poison)
Full Attack: Bite +22 melee (1d4-1 plus poison)
Space/Reach: 2 ft./0 ft.
Special Attacks: Poison
Special Qualities: Construct traits, darkvision 60 ft., familiar traits, low-light vision, SR 20
Saves: Fort +9, Ref +12, Will +14
Abilities: Str 8, Dex 16, Con , Int 13, Wis 12, Cha 7
Skills:* Hide +20, Listen +10, Spot +10
Feats: Ability Focus (poison), Improved Initiative
Environment: With Warped One master
Organization: With Warped One master
Challenge Rating: 3
Treasure: None
Alignment: As Warped One master
Advancement: -
Level Adjustment: -
*Use the familiar's skill ranks or its masters, whichever are better.

This homunculus was crafted with 6 HD. As a familiar, many of its statistics reflect its master's statistics.

In battle the homunculous attacks at its master's direction, generally attempting to poison enemy spellcasters.

Familiar Abilities (Ex)
As the familiar of a 15th-level wizard (Alertness, improved evasion, share spells, empathic link, deliver touch spells, speak with master, spell resistance, scry on familiar). As an Improved Familiar a homunculus familiar does not gain the speak with animals of its kind ability.

Poison (Ex)
Injury, Fortitude DC 21, initial damage sleep for 1 minute, secondary damage sleep for another 5d6 minutes. The save DC is Constitution-based and includes a +2 racial bonus, the bonus from Ability Focus, and is based on the Warped One's class level.