There's two or maybe three abilities depicted there. Some sort of splitting into more copies, and the ability to grow more limbs; mainly for natural weapons but flight is an option if the PCs try the flying out of reach trick. And maybe the ability to cause insanity in viewers.
Maybe it can generate copies or grow new limbs as a move action which can be combined with an actual move - that little lamb never stops moving.
Qlippoths have horrific appearance (a passive gaze attack, basically) with a wide variety of effects. If you want Wis damage (Int damage seems like it might accidentally KO animal companions too fast) that's a reasonable 'aura' effect.
Crit immunity, sure. Amorphous is the name of the monster ability you want. Coup de grace only works on enemies not immune to crits anyway.
If you crit on this, more copies pop out.
Offspring of Shub-Niggurath.
https://pathfinderwiki.com/wiki/Shub-Niggurath
That's pretty decent. Here's what I came up with:
Lamb of Niggurath:
CE Small Abberation
Init +8; darkvision 60 ft.; all-around vision, Perception +19; Aura: horrific appearance (30 ft., DC 23)
AC 25, t17, ff18
108hp
Fort +12, Ref +12, Will +10
Amorphous, DR 10/lawful; Immune cold, acid, mind-affecting effects, polymorph effects; Regeneration 2 (lawful), SR 18
Speed 40 ft.
2 slams +11 (1d3+1)
Spell-Like Abilities (CL 12th)
Constant—freedom of movement, true seeing
Str 13, Dex 18, Con 26, Int 13, Wis 19, Cha 20
Base Atk +11; CMB +17 (+21 grapple); CMD 34 (42 vs. trip)
Feats Combat Reflexes, Dodge, Improved Initiative, Iron Will, Mobility, Multiattack, Power Attack
Skills Acrobatics +23, Climb +23, Bluff +20, Disguise +20 (+35 as a lamb, goat or fawn), Intimidate +30, Fly +19, Perception +19, Stealth +23, Swim +16
Languages: telepathy 100 ft.
Adaptive Mutation (Su): every round as a swift action, a Lamb of Niggurath may select mutations worth up to 1d4+4 points from the table below:
- +20ft base speed 1pt
- Climb 20ft 1pt
- Fly 60ft (clumsy) 4pts
- increase one size category* 1pt
- increase natural reach by 5ft* 1pt
- +2 Str* 1pt
- +2 Dex* 1pt
- add one slam attack* (base damage 1d3) 1pts
- add one bite attack* (base damage 1d6) 2pts
- increase base damage of one type of natural attack by one step* 1pt/attack affected
-Split (see ability below) 3pts
*this ability can be chosen multiple times, even on the same turn.
A typical Lamb of Niggurath may have a maximum of 25 points worth of mutations at one time. If a Lamb of Niggurath would choose a mutation that would put it over this limit, the newest mutation replaces another of equal or greater value of the Lamb of Niggurath's choice.
Disjointed Step (Ex): a Lamb of Niggurath has a +4 dodge bonus to AC as well as a +4 competence bonus to Acrobatics and Reflex saves
Horrific Appearance (Su):
Creatures that succumb to a Lamb of Niggurath's horrific appearance take 1 Wisdom bleed for 2d4+4 rounds
Split (Su): any time a Lamb of Niggurath takes damage from a slashing or piercing weapon, or any time it chooses to do so with it's Adaptive Mutation ability, a new monstrosity is formed from the severed limb or crawls forth from the wound. These creatures use the statistics from the monsters on the list of Summon Monster III, though they all bare some vague and disturbing relationship to their progenitor.
A random mental ability damage is a good substitute for a madness score. The shepherd who tries to slaughter this thing is probably turned into a drooling wreck.
I think the changes are permanent, but it can choose to loose mutations at the same rate it normally gains them, so it can go back to being a sweet little lamb after it eats you.
The horrific appearance really isn't doing it for me. Maybe it staggers you for 1d3 rounds and each round you take 1d4 Wisdom, and then you're shaken for 1 minute. If you succeed, you're shaken for 1d3 rounds.
I think Wisdom is the key, though. It drives you crazy, not stupid.
Ok, It's Silver Diamond's pet.