Here's a preliminary stat block...
Demon, Death (Ostego)
Large Outsider (Chaotic, Evil, Extraplanar)
Hit Dice: 7d8+x (x hp)
Initiative: +x
Speed: 30 ft. (6 squares), fly 60 ft. (average?)
Armor Class: x (–1 size, +x Dex, +x natural), touch x, flat-footed x
Base Attack/Grapple: +7/+11 plus Str
Attack: Claw +x melee (xdx+x plus paralysis)
Full Attack: 2 claws +x melee (xdx+x plus paralysis) and bite +x melee (xdx+x plus poison)
Space/Reach: 10 ft./10 ft.
Special Attacks: Adamantine claws, spell-like abilities, summon demon (?)
Special Qualities: Damage reduction ?, darkvision 60 ft., immunity to ?, resistance to ?, spell resistance ?, telepathy 100 ft.
Saves: Fort +x, Ref +x, Will +x
Abilities: Str x, Dex x, Con x, Int x, Wis x, Cha x
Skills: x
Feats: 3
Environment: Infinite Layers of the Abyss
Organization: Solitary, pair, or squad (1–4)
Challenge Rating: x
Treasure: Standard(?)
Alignment: Always chaotic evil
Advancement: 8–14 HD (Large); 15–21 HD (Huge)
Level Adjustment: +?