Urdlen
The Crawler Below

Demon Lord of Blood, Malice and Depths (Gnome pantheon) [Intermediate]

Symbol White mole  
Alignment Chaotic Evil  
Priest Alignment CE, NE, LE  
Plane Abyss  
Worshippers Thieves, assassins, warriors, the insane  
Race Gnome (evil gnomes only)  
Sex Any  
Attributes Constitution 13, Charisma 12 or less -1
Proficiency Groups Rogue, Priest, General 5
Bonus Proficiency Mining 5
Preferred Weapon Dagger, knife  
Allowed Weapons As thief 5
Armor Any, any shield  
Primary Sphere Chaos 8
Major Spheres All, Combat, Elemental (earth), Healing (reverse), Protection, Sun (reverse) 41
Minor Spheres Divination, Elemental (fire), Necromantic 15
Additional Spells Cloak of Fear (4th level), Find the Path (6th level), Know Direction (1st level), Mindshatter (5th level) 2
Abilities
  Control Undead at 1/2 level (rounded up) 10
  No followers  
  Every 3rd spell of a spell level may be chosen from the Wizard school of illusion of 1 level lower (so Phantasmal Force could replace the 3rd second level spell of a priest)
25 (base) - 10 (reduced access) = 15
15
5th level Blur (1/day)
5 (1/day) + 4 (W2) - 2 (5th level) - 3 (4 powers) = 5 (minimum)
5
7th level Cloak of Fear (1/day)
5 (1/day) + 4 (P4) - 3 (7th level) - 3 (4 powers) = 5 (minimum)
5
10th level Cause Insanity by touch (1/day)
5 (1/day) + 5 (P5, as mindshatter) - 4 (10th level) - 3 (4 powers) = 5 (minimum)
5
14th level Feeblemind by gaze (1/day)
5 (1/day) + 10 (W5) - 6 (14th level ) -3 (4 powers) = 6
6
  Rot plants by touch (1-6 hp per touch plus an additional 1 hp/round for 7-10 rounds)
Treated as a 15 point power
9
Limitations
  Priests of Urdlen cannot cast any spell that creates or otherwise summons a living creature or plant  
  Hit points (d6) as thief -10
  Fanatic: priests of Urdlen despise all other priests and priest-like classes -5
Raiment Bare head, white cloak  
Animal Albino mole  
Holy Days Winter solstice (the blood of living sacrifices, both human and animal, jewelry)  
Notes
Urdlen despises all other gnome gods, as well as all green plants
Many priests of Urdlen are multi-classed priest/thieves, and most are insane
Worship of Urdlen is performed in unlit natural caverns
Animals can sense the presence of a priest of Urdlen, their reaction grows more and more negative with each level attained
Spriggans do NOT worship Urdlen
Background
Spawned of the stuff of nightmares, Urdlen is the gnome's worst fears given life: an insane, ravening creature, full of hatred and lust for the blood of any living things. It is said to be the offspring of Segojan Earthcaller and the Queen of Succubi, grown into a malevolent beast that is half god and half lord of the Abyss. Urdlen rules its own layer of the Abyss, an unending expanse of twisted tunnels and dark chasms.

Few gnomes worship Urdlen, and those that do are always evil and usually insane. It demands a constant supply of blood from its worshippers -- soaked into the earth from fresh kills. Jewelry and other precious works are also to be sacrificed to it, by beating and smashing them until their value is destroyed. Urdlen hates all livings things, and barely tolerates its own priests -- more than one has met an unpleasant end after his usefulness was ended.

Urdlen is one of the few demon lords who needs neither talisman nor communion to grant spells. Sages speculate that this is a combination of its divine heritage and its lust for blood -- the blood of each sacrifice helps forge the bond back to its priests. It is worth noting that priests who are delinquent in their sacrifices cannot regain spells -- those that survive this insult, at least.

Sources
Dragon #61: The Gnomish Point of View (original source, reprinted in Best of Dragon vol. III)
Monster Mythology, p.37
Unearthed Arcana, pp. 117-118, 122
Urdlen as a demon lord is my own concept, as is his ancestry