Living Sets are akin to living spells, but rather than being manifestations of magic they are manifestations of Law. As such, most living sets are either LE, LN, or LG and only in rare cases are they chaotic. Each living set has some assortment of magical abilities which it uses in its chosen mission. They cannot be seen save by spells such as true-seeing, which reveal an amobea like creature formed from light. Geometric crystals sparkle within its body, flickering with their own energies. Sets vary in color and size as well. The origin of living sets is unclear, some believe they arise from the plane of Mechanus, others suspect the hand of the mysterious Axioms. The beings may come from Mechanus, but they are found across the planes though they are incredibly rare to the point many believe members to be unique.

Legends speak of a group of marraenoloths who, tainted by the greed of their race, sought to find the Axioms and use an artifact in their possession to usurp their power. Somehow, these planar travelers managed to find the hidden kingdom of the Axioms who emerged from their immaculate dwellings of perfect geometries. Upon seeing the indescribable beauty of those who are Foundation of All Things, the marraenoloths surrended without a battle and begged only to serve.

Entrope
With a rending gnashing sound the great beast turns an insectile head towards your party, before diving into the ground beneath your feet. A sudden sound of vaccume and wind rushes past as you stare into the void of another plane, the tail end of the segmented worm writhing in the distance.

Without stopping a Tanzu’s actions any ecosystem would be damaged and eventually completely collapse, which brings this odd species of outsider in firm conflict with many a Druid on the Prime.
Large outsider
Hit dice: 8d8+40 (76hp)
Initiative: +3
Speed: 40 feet, climb 30 feet.
Armor class: 24 (-1 size, +3 Dex, +12 natural)

There is a large frog-like creature the size of a cat sitting in the corridor ahead of you. As it notices you it begins to inhale, swelling rapidly and disturbingly. . . Tiny Magical Beast

Planescape Survival Guide (the handy-dandy guide, not the comic ) #1, Beholders:

 

LevelHDBABFort
RefWillSkill Points
Special 1st1d8+1+2
+2+2(8+Int)

Not really directly related to Planescape but in one my articles about the Istaritu I referred to a creature known as a Hu Xian, as one of the NPCs was one. Anyways I have stats of these lying around for a while. I updated them a bit, to see if the *New* stat format they're using is any good.This is actually a conversion of an old D&D monster...HU XIAN

Small Outsider (Evil, Extraplanar) Hit Dice: 5d8-5 (18 hp) Initiative: +9 Speed: 30 ft Armor Class: 20 (+1 size, +5 Dex, +4 natural), touch 16, flat-footed 15 Base Attack/Grapple: +5/+1 Attack: Bite +10 melee (1d8) Full

Medium Outsider (Extraplanar) Hit Dice: 4d8+8 (26 hp) Initiative: +1 Speed: 30 ft. Armor Class: 15 (+1 Dex, +2 natural, +2 deflection), touch 13, Base Attack/Grapple: +4/+5 Attack: Slam +5 melee (1d4+1) or hand axe +5 melee (1d6+1/x3)