Shadow Asp (CR 1)

Tiny Magical Beast
Alignment: Always neutral
Initiative: +5 (Dex); Senses: darkvision 60 ft., low-light vision, Listen +7, and Spot +7

AC: 19 (+2 size, +5 Dex, +2 natural) touch 17, flat-footed 14
Hit Dice: 1d10+2 (7 hp)
Fort +4, Ref +7, Will +1
Speed: 30 ft., climb 10 ft.
Space: 2 1/2 ft./0 ft.
Base Attack +1; Grapple +9
Attack: Bite +8 melee
Full Attack: Bite +8 melee
Damage: Bite 1d3-2 plus poison
Special Attacks/Actions: Create spawn, poison
Abilities: Str 7, Dex 21, Con 15, Int 4, Wis 12, Cha 10
Special Qualities: incorporeal form
Feats: Weapon Finesse
Skills: Climb +6, Hide +16, Listen +7, Move Silently +6, and Spot +7
Advancement: 2-3 HD (Small)
Climate/Terrain: Any tomb or underground
Organization: Solitary or clutch (3-12)
Treasure/Possessions: 50% coins, 50% goods, 50% items

Source: Fiend Folio

Create Spawn (Su): A creature slain by a shadow asp's poison rises as a shadow in 1d2 days. Such a shadow is considered uncontrolled, but it is bound to the area, usually a tomb or crypt, as a guardian, unable to stray more than 100 feet from the spot where in was first spawned.

Poison (Ex): A shadow asp delivers its poison (Fort DC 12 negates) with each successful bite attack. Initial and secondary damage are the same (1d6 Str).

Incorporeal Form (Su): A shadow asp can become incorporeal for up to 1 hour per day. It can activate this ability at will (a free action), and the time of use need not be continuous. While incorporeal, a shadow asp's Armor Class is 17 (2 size, +5 Dex). The shadow asp cannot deal damage to corporeal opponents. The creature has a 50% chance to ignore any damage from a corporeal source, except for force effects or attacks made with ghost touch weapons. An incorporeal shadow asp can pass through solid objects, but not force effects, at will. Its attacks ignore natural armor, armor, and shields, but deflection bonuses and force effects work normally against them. A shadow asp always moves silently while incorporeal and cannot be heard with Listen checks if it doesn't wish to be.

Skills: A shadow asp has a +10 racial bonus on Hide checks due to its natural camouflage, and a +5 racial bonus on Listen and Spot checks due to its natural vigilance. Shadow asps also have a +8 racial bonus on Climb checks and can always choose to take 10 on Climb checks, even if rushed.

Shadow asps are smarter than normal snakes, and anyone observing their tactics can easily see this. They use their ability to become incorporeal to mob intruders in the tombs they're set to guard, emerging to bite from the walls, floors, and even ceilings. They prefer to bite and then flee, instinctively aware that their venom takes time to work, then returning to strike and flee again. They are often accompanied in battle by the shadows of slain intruders of the past.