[How to make a niche for the unloved phasm, the monster whose only power is to turn into other monsters? Two thoughts. One: make it better at turning into other monsters than anything else. Two: make it a goo boy or girl, a monster type super popular on the internet, but under-served by tabletop RPGs. I chose this image because it seems very transitional.]
Sometimes called “protein polymorphs”, phasms are strange and mercurial creatures that delight in assuming a myriad of forms. They are hedonistic by nature, adopting forms that allow them to experience new sensations or live lives of luxury. They are especially fond of assuming mortal shape and indulging in all manner of vices, then escaping before they have to face any consequences.
Phasms are frequently looking for new information, sensations and forms to assume. Those that offer any of these to a phasm can usually parley their way out of combat. If forced into combat, a phasm will shift effortlessly between shapes designed to terrorize and inflict as much damage as possible. Phasms will not hesitate to flee from a fight, often adopting a flying or swimming form to do so.
The origins of phasms are unknown, and most phasms will gladly weave a dozen contradictory tales if asked. Some sages speculate that they are an advanced form of doppelganger, and phasms do frequently associate with doppelgangers as partners in crime and convenient decoys. Others propose an ooze given life by demonic or protean forces, the spawn of a Great Old One, or even sentient particles of the plane of Limbo.
The average phasm is capable of assuming the forms of humanoids or beasts, but advanced phasms add more variety of shapes to their repertoire. Especially old and powerful phasms can take any form allowed by the shapechange spell, and some wicked phasms can even assume undead form (as per undead anatomy IV)
Phasm CR 8
XP 4,800
CN Medium aberration (shapechanger)
Init +5; Senses darkvision 60 ft., Perception +21, scent, tremorsense 60 ft.
Defense
AC 20, touch 15, flat-footed 14 (+5 Dex, +1 dodge, +4 armor)
hp 105 (14d8+42)
Fort +11, Ref +13, Will +17
Defensive Abilities amorphous, eerie grace; Immune disease, paralysis, poison, stunned
Offense
Speed 30 ft.
Melee slam +13 (2d6+4)
Space 5 ft.; Reach 10 ft.
Special Attacks fearsome form
Spell-like Abilities CL 14th, concentration +18
Constant—mage armor
Statistics
Str 17, Dex 20, Con 16, Int 16, Wis 19, Cha 18
Base Atk +10; CMB +13; CMD 29
Feats Blind-fight, Combat Expertise, Combat Reflexes, Dodge, Mobility, Spring Attack, Whirlwind Attack
Skills Bluff +18, Diplomacy +18, Disguise +18 (+28 when using change shape), Intimidate +21, Knowledge (arcana) +20, Knowledge (local) +17, Perception +21, Sense Motive +18, Stealth +22
Languages Aklo, Common, Draconic, telepathy 100 ft.
SQ change shape (animal, humanoid or magical beast, alter self or beast shape IV), compression, perfect copy, quick change
Ecology
Environment urban or underground
Organization solitary
Treasure standard
Special Abilities
Eerie Grace (Su) A phasm gains a resistance bonus on all saving throws equal to its Charisma modifier.
Fearsome Form (Ex) When using change shape, a phasm’s natural weapons are all larger and more developed than the base creature. It gains Improved Natural Attack as a bonus feat for each of its natural weapons when assuming a different form. In a form that lacks natural weapons, it gains a slam attack that deals 1d4 points of damage (for a Medium form).
Perfect Copy (Ex) A phasm can assume the appearance of an individual creature when using its change shape ability
Quick Change (Ex) A phasm can use its change shape ability as a move action.