Here's an idea
Akasetsu
Colossal Magical Beast
Hit Dice: 50d8+700 (900 hp)
Initiative: +18 (+14 Dexterity, +4 Improved Initiative)
Speed: 160 ft. (12 squares), climb 160 ft., fly 320 ft. (perfect), swim 160 ft.
Armor Class: 55 (-8 size, +14 Dex, +39 natural armor), touch 16, flat-footed 41
Base Attack/Grapple: +50/+88
Attack: Coil whip +72 melee (4d6+22) or spit venom +63 ranged (blindness and stun)
Full Attack: Coil whip +70 melee (4d6+22) and bite +68 melee (4d6+11 plus poison) or coil whip +70 melee (4d6+22) and spit venom +61 ranged (blindness and stun)
Space/Reach: 100 ft./65 ft. (30 ft./20 ft. when coiled)
Special Attacks: Charming gaze, constrict 4d6+33, improved grab, poison, spells
Special Qualities: Archivist abilities, chameleon ability, damage reduction 25/epic, darkvision 60 ft., flight, low-light vision, scent, spell resistance 60, tremor sense 60 ft.
Saves: Fort +51, Ref +51, Will +47
Abilities: Str 54, Dex 39, Con 39, Int 42, Wis 42, Cha 42
Skills: All skills at +53 plus ability modifiers and miscellaneous modifiers.
Feats: Combat Casting, Eschew Materials (b), Improved Counterspelling, Scribe Scroll, Silent Spell, Still Spell
Epic Feats: Epic Spellcasting, Ignore Material Components, Polyglot, Scribe Epic Scroll
Divine Abilities: Maven, Omnicompetent
Environment: Any subterranean
Organization: Solitary, pair, or nest (3-4)
Challenge Rating: 50
Treasure: Standard + Archives
Alignment: Usually neutral evil
Advancement: 51-63 HD (Colossal); 64-127 HD (Titanic); 128-150 HD (Macro-Fine)
Level Adjustment: +75
As you enter the stone chamber you cannot help but feel that you are not alone. In the darkness that surrounds you there is naught but silence, though the scent of the crypt seems strangely subdued. As you tremble forward, leering emerald eyes, loom up out of the shadows and into the light of your torch, gleaming with the malice of untold ages and the sinister wisdom of forgotten lore. Coiling around you, it's disarming gaze invites you, welcoming you into it's embrace, all the while crushing you within it's coils.
Akasetsu are extremely powerful cobra-like serpents. Lurking in forgotten tombs and subterranean lairs, they while away the time by studying the secrets of the dead. Considered by many cultures to be the keepers of dusty tomes and moldy remnants of times long since past, they are often sought out for information, though more often than not, such seekers often become the akasetsu's latest meal and their bones are used to fortify the structures in which the akasetsu dwell.
Akasetsu know and speak all languages.
Akasetsu are 100 ft. long, with a 5 ft. diameter, and weigh 900 tons (1,800,000 pounds), due to their incredible muscular density.
Combat
Akasetsu prefer subtlety to stupidity and will always avoid direct confrontation if at all possible, though if a threat is perceived to be dangerous enough for the akasetsu to become concerned for it's own safety, it will either destroy the threat personally, using it's most devastating abilities, or flee if it feels the threat is too great to deal with. It is important to note that, although they are more than capable of doing so, akasetsu never swallow prey whole unless they are absolutely sure their prey is dead.
An akasetsu’s natural weapons are treated as epic for the purpose of overcoming damage reduction.
Archivist Abilities (Ex): Akasetsu are skilled archivists and possess 25th-level Archivist abilities, these abilities are equivalent to half their Hit Dice (rounded down). For more details concerning Archivists, consult Heroes of Horror.
Spells: As 25th-level Archivist (Caster level 50th; 4/9/9/9/9/8/8/8/8/7; Epic Spells Per Day: 5). The save DC is Wisdom-based. As each akasetsu is a unique individual with their own motives and personality, there truly is no typical selection of spells that they memorize each day.
Chameleon Scales (Ex): Because of it's everchanging scales, an akasetsu blends in with it's surroundings, gaining a +10 circumstance bonus on Hide checks.
Charming Gaze (Su): An akasetsu's gaze functions like the mass charm monster spell against creatures withing 90 ft. (Will DC 51 negates). The save DC is Charisma-based.
Constrict (Ex): An akasetsu deals 4d6+33 points damage with a successful grapple attack against a Huge or smaller opponent.
Flight (Su): An akasetsu can fly as though with a fly spell at 360 ft. with perfect maneuverability. This ability grants it a +6 circumstance bonus on Move Silently checks when flying.
Improved Grab (Ex): To use this ability an akasetsu must hit with it's bite or coil whip 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.
Poison (Ex): Bite, Fortitude DC 49; initial and secondary damage 5d8 Constitution. The save DC is Constitution-based.
Prehensile Tail (Ex): An Akasetsu has an extremely dexterous prehensile tail that can be used to perform any task that could otherwise be performed with a single hand. Including, though not limited to, pointing, turning pages, wielding a tool or weapon, and scratching one's head in confusion.
Spit Venom (Ex): Akasetsu can spit their venom up to 240 ft. distant at a single target. A successful strike with this attack causes the target to be blinded and stunned by the shock and pain. They will remain stunned for 1 round, and will be blinded until they take 1 minute (10 rounds) to rinse their eyes out with water.
Skills: Akasetsu have a +4 racial bonus on Hide, Listen, and Spot checks and a +8 racial bonus on Balance and Climb checks. An akasetsu can always choose to take 10 on a Climb check, even if rushed or threatened. An akasetsu has a +8 racial bonus on any Swim check to perform some special action or avoid a hazard. It can always choose to take 10 on a Swim check, even if distracted or endangered. It can use the run action while swimming, provided it swims in a straight line.
Listed as Chaotic, but acting quite Neutral in the description given.
