Armor Class: 7 
Hit Dice: 3
Attacks: Tentacles (1d6)
To Hit Bonus: +3
Saving Throw: 16
Special: Toxin (save or paralyzed 1d6 rounds), Surprise on 1-5, 1/2 damage from blunt weapons.
The Tunnel Stalker is a man-sized gastropod, silent and swift-moving, that is a danger of the undercity. The slug-like creature has a thick, slimy, rubbery hide, and at one end of its body is a mass of tentacles, two of which can extend to a length of nearly ten feet. These long hunting tentacles end in a mass of barbed stingers that inject a powerful neurotoxin that paralyzes a foe and causes burning pain and can, over time and multiple doses, slowly digest tissue into a soft, pulpy mass for the Tunnel Stalker to devour.
The Tunnel Stalker's thick skin is filled with chromatophores, allowing it to easily camouflage itself against its surroundings, and its nature allows silent movement. The creature may climb walls and ceilings, and often attacks from ambush.
Tunnel Stalkers are cowardly with animal instinct but great cunning. They tend to attack lone prey, stragglers, sleeping characters, or other easy prey. They avoid fire, electricity or other similar dangers.
Armor Class: 4 
Hit Dice: 4
Attacks: Claws (1d6+2)
To Hit Bonus: +4
Saving Throw: 15
Move: 12, Climb 12, Jump 6
Special: Invisible at will.
Umbrans were agents of the ancient Empire of Ylum, enforcers of their will, spies, and assassins of the first order. Arcane constructs, these things look like a mix of spider and mantis with cold, featureless faces and long, hooked forelimbs. They can climb walls, move silently, and survive in nearly any climate.
They may turn invisible at will, and usually move about invisibly. They communicate with each other telepathically, though they may communicate is a low chatter that sounds like whispered clicks when they wish to communicate with their masters.
The Umbrans that survive do so either as guardians of the secrets of Ylum or as agents of long-lost schemes to revive the Witch-Kings. As such, the Umbrans may be acting for a new master, often one who has become an agent of the long-dead Witch-Kings.
(And yes, I'm stealing from Babylon 5 now.)