I'll join in the fun
I bent the rules a bit on Epic-levels-don't-add-to-HD (as did others), but it does seem to make up for a bit of the 10 PL score... Also, the no-save soulgobbler surprised me too, but it came straight from the CC conversion, and that's the way the original Tomb module has it too. Don't come within 60 feet, I guess

By Edena's notes, he's meant to rank above 300th level.
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Acererak, the Devourer
Cambion Demilich Necromancer 20/Cleric 20(Death, Evil)/True Necromancer 10/Master of Shrouds 10/Archmage 5/Epic 150
Large Undead (Chaotic, Evil)
HD: 215d12 (1180 hp)
Initiative: +9 (+5 Dex +4 Improved Initiative)
Speed: fly 60 ft (perfect)
AC: 50 (-1 size, +5 Dex, +36 natural)
Special Attacks: Howl, Trap the Soul, Curse, Fear Aura
Special Qualities: Undead, Spell Immunity, Turning Immunity,
Weapon Immunities, Susceptibilty, SR 40, Blindsight 400 ft,
Zone of Desecration.
Saves: Fort --(+84), Ref +73, Will +118
Abilities: Str 24, Dex 20, Con -, Int 68, Wis 38, Cha 42
Feats: 52 in total; all Metamagic, Improved Initiative, Spellcasting Prodigy, Spell Focus (Necromancy), Greater Spell Focus (Necromancy), Even Greater Spell Focus (Necromancy), Pretty Darn Massive Spell Focus (Necromancy), Unthinkably Vast Spell Focus (Necromancy), Spell Focus Even Greater Than The Last One Which Was Really Quite Great Already I Think Everyone Will Pretty Much Agree (Necromancy). Spell Penetration, Greater Spell Penetration, Extra Turning, Empower Turning, Heighten Turning, etc...
Acererak was born thousands of years ago, from the union of a human woman and the Balor Lord Tarnhem. Both child and mother survived birth, and his childhood progressed much as any other child's. However, persecution over his cambion nature eventually drove all feelings of love or mercy from his being, and he became an icy cold and bitter creature. After attaining mastery as a necromancer under the tutelage of Tenebrous himself, he made the transformation into lichdom, as the first step of a far more transfigurative process. For these centuries, he has been preparing the ritual of his Apotheosis, when he would join with the Plane of Negative Energy itself and gain utter control over all undeath in the multiverse. That time is now nearing completion.
His original body has long crumbled to dust, but Acererak's essence can take control of any undead guise it wants. Currently, his form is that of a large, horned, floating Titan's skull. The eyesockets and have been fitted with large ruby jewels, and its teeth have been likewise replaced. For the first time in centuries, the Demilich has returned in tangible form to a material plane, to harvest the countless souls of the coming conflict and complete his transformation.
COMBAT
Acererak, as a True Necromancer, casts Necromancy spells at caster level 65, and rebukes undead as a 40th level cleric (controlling any of 20HD or less automatically). He has poured many of his Epic level research into learning to cast spells at progressively higher levels, and has slots up to 60th level. He has access to True Dweomers of 10th level.
As a giant, floating, disembodied skull, Acererak wears no items. If he needed to, he could easily take a shape that can use them.
Howl (Su): Once per round, 20-foot radius, Fortitude save (DC 58) negates; Irrevocably slain on a failed save. Short of a god’s magic, a true resurrection or miracle cast by a 20th-level cleric or a wish cast by a 20th-level wizard or sorcerer is the only magic that can raise a creature slain in this manner.
Trap the Soul (Su): Once per round, 60-feet, as trap the soul cast by a 20th-level. No save to avoid. Spell resistance is likewise ineffective.
The soul is drawn into one of the gems contained in the skull. The victim’s body immediately crumbles to dust.
If the skull is destroyed, each trapped soul receives a Fortitude save (DC 35). Those that fail the save are irrecoverable, devoured by the demilich. A successful save means the creature’s soul is still present in the gem. The soul can be freed by crushing the gem, though a material body (clone, simulacrum) must be present and within 30 feet of the gem when it is crushed. A soul released when no receptacle is present is lost forever.
Curse (Su): Once per round (and only when all gems are filled), the demilich can unleash a powerful curse on all creatures within 20 feet; such as, always hit in combat by any attacking opponent, never succeed at a saving throw, never gain XP from creatures slain or treasure gained, or something equally as powerful. The curse can be removed with a remove curse, but the victim loses 1 point of Charisma permanently when the curse is removed.
Fear Aura (Su): All within 60 feet; Will save (DC 42) or flee in fear for 2d6 rounds. If the save is successful, that creature cannot be affected again by Acererak’s fear aura for one day.
Rejuvenation (Su): When destroyed, Acererak will reform at full strength in 1d10 days unless his phylactery is also destroyed (it is concealed in his Fortress of Conclusion, adrift in the dark heart of the Negative Energy Plane).
Spell Immunity (Ex): The only spells that can affect a demilich are dispel evil (deals 1d4+4 points of damage), hallow or halt undead (causes the skull to simply hover for 1 round), shatter (deals 3d6 points of damage), power word kill (works normally if cast by an astral or ethereal caster), and holy word (deals 5d6 points of damage).
Weapon Immunities (Ex): The demilich is immune to all weapon attacks save for the following, which deal normal damage: A barbarian, fighter, or ranger wielding a vorpal weapon or weapon of +5 or greater enchantment; a paladin with a vorpal weapon or weapon of +4 or greater enchantment.
Any other creature wielding a weapon with a +4 or greater or a disruption weapon can deal 1 point of damage per successful attack. Note the demilich is immune to the disruption power of the weapon.
Lich immunities: Immune to mind-influencing effects, poison, sleep, paralysis, cold, polymorph, stunning, and disease. Not subject to critical hits, subdual damage, ability damage, energy drain, or death from massive damage.
Zone of Desecration (Su): Acererak is always surrounded by a 650-ft area of Negative Energy. It is otherwise identical to the Desecrate spell.
High Arcana: Mastery of Counterspelling, Arcane Fire, Spell Power +6.