Mercurial Spider (CR 1)

Tiny Construct
Alignment: Any (same as creator)
Initiative: +3 (Dex); Senses: Spot +6
Languages: Cannot speak

AC: 17 (+2 size, +3 Dex, +2 natural), touch 15, flat-footed 14
Hit Dice: 2d10 (11 hp)
Fort +0, Ref +3, Will +0
Speed: 20 ft., climb 10 ft.
Space: 2-1/2 ft./0 ft.
Base Attack +1; Grapple -10
Attack: Bite +6 melee
Full Attack: Bite +6 melee
Damage: Bite 1d3-3 plus poison
Special Attacks/Actions: Poison
Abilities: Str 5, Dex 17, Con -, Int 2, Wis 10, Cha 2
Special Qualities: Construct traits, familiar traits, fluid form
Feats: Weapon Finesse
Skills: Climb +11, Hide +15, Move Silently +6, and Spot +6
Climate/Terrain: Any
Organization: Solitary
Treasure/Possessions: None

Source: Dragon #341

Fluid Form (Su): The mercurial spider may mimic the form of any Tiny inanimate object. This ability is like the spell statue, except that the spider may adopt any form and it does not gain hardness through the use of this ability. This transformation lasts until the spider wills it to end or upon its destruction.

This ability also allows a mercurial spider to pass through small holes or even cracks without slowing its speed. As long as the opening allows the passage of liquid, the spider can slide through the hole.

Poison (Ex): Injury, Fortitude DC 11, initial and secondary damage 1d6 Str. The save DC is Constitution-based.

Skills: Mercurial spiders have a +4 racial bonus on Hide and Spot checks and a +8 racial bonus on Climb checks. A mercurial spider can always choose to take 10 on Climb checks, even if rushed or threatened. Mercurial spiders use either their Strength or Dexterity modifier for Climb checks, whichever is higher.

The mercurial spider prefers to attack incapacitated foes and uses its fluid form ability to get close to sleeping or otherwise unaware victims. For this reason they prove the familiar of choice for those involved in plots and assassinations.