This isn't entirely clear about the imprinting, but I gather that Mossmutter gets spell-casting abilities from controling the "incomplete imprints" of the skin puppets somehow.
Ok, here's my question: do we want to do Mossmutter and skinpuppets as single-adventure "unique monsters" or make a false Keraptis template and allow other mold wyrms to create skin puppets?
There are four False Kerapti in
Return to White Plume Mountain and, as you may have gathered by now, they are an integral part of the plot. A long time ago, a wizard named Keraptis found a way to store imprints of himself on scrolls. These are either complete or partial "K-imprints". All four of the False Kerapti have absorbed a complete K-imprint, which makes them think they are the wizard Keraptis. All of the False Kerapti have the ability to absorb subsumed minds into their hierarchical minds. Subsumed minds are created when someone absorbs a partial K-imprint -- after a few months, they become a husk and fall under the control of one of the False Kerapti.
The other three False Kerapti are a gnome, an ogre mage and an efreet, so they aren't quite as... special as Mossmutter. While the other False Kerapti gain subsumed minds from partial imprint victims, Mossmutter's subsumed minds are all Skin Puppets, created by his spore cough. In other words, Skin Puppets are the particular manifestation of Mossmutter's spore cough/spore blight abilities, as a result of him being a False Keraptis.
Here is the write up for the False Keraptis "template":
Developing a New False Keraptis
A DM wishing to create additional False Kerapti (or establish a former PC as a new NPC False Keraptis) can use the following guidelines to establish the character’s abilities.
A new False Keraptis can generate spell effects as a 12th-level wizard, in addition to using his or her regular powers and abilities. At the time of imprinting, the DM must choose a daily complement of spells (four 1st-level, four 2nd-level, four 3rd-level, four 4th-level, four 5th-level, and one 6th-level) for the new pretender. Available choices include spells from the character’s own spellbook or priest sphere (if applicable), plus the following list, which represents the contents of the original wizard’s spellbook: 1st-charm person, K: complete imprint*, magic missile, sleep, wizard mark; 2nd-acid arrow, continual light, darkness 15’ radius, ESP, knock, magic mouth, mirror image, wizard lock; 3rd-dispel magic, fireball, fly, lightning bolt, monster summoning I, slow, tongues; 4th-charm monster, dimension door, enchanted weapon, Evard’s black tentacles, ice storm, improved invisibility, monster summoning II, polymorph other, polymorph self, stoneskin, wind wall, wizard eye; 5th-advanced illusion, cloudkill, cone of cold, conjure elemental, dismissal, monster summoning Ill, true seeing, force, wall of stone; 6th-contingency, death fog, death spell, globe of invulnerability, monster summoning IV, Tenser's transformation. (Spells of 7th level and higher become available to a False Keraptis who reaches a level high enough to be able to cast them.) Once the DM has decided upon a spell selection, it becomes permanent. (No such choices exist for a husk who becomes the new seat of an existing hierarchical mind; he or she simply assumes the existing spell complement.)
Like the other False Kerapti, the new pretender can channel spells through his or her husks, see through their
eyes, speak through their mouths, and direct their actions.
*
Note: A
K: complete imprint incorporates all the partial K-imprints, granting the host the standard uses/day of each and enabling him or her to scribe these sentient spells on scrolls as desired.
The Existing False Kerapti
Each of the four False Kerapti currently residing in White Flume Mountain calls himself Keraptis, as do the troops loyal to him. However, each pretender and his minions refer to the other False Kerapti as ”usurpers,” or by the names the Resistance leader Nix has given them (Nightfear, Spatterdock, Killjoy, and Mossmutter).
All four False Kerapti believe Wave, Whelm, Blackrazor, and Frostrazor to be their personal property. Should the PCs openly display any one of them in front of a False Keraptis, the pretender demands that they surrender it immediately. No alliances are possible unless they do so, and attempts to bargain only precipitate attacks.
Abilities
Each False Keraptis gained the full spellcasting capabilities of a 12th-level wizard, in addition to the full personality of Keraptis, upon memorization of a K: complete imprint. However, as none of the K-imprints were perfect copies of the original mind, large sections of each pretender’s “memories” are hazy or altogether absent.
All the spells granted by the K: complete imprint are usable as spell-like abilities once per day, with no verbal, somatic, or material components required. Furthermore, each pretender can channel spells through his vessels at a rate of one spell per three subsumed minds per round. (These vessels must be within 10 feet of each other, but can be at any distance from their leader.) Channeled spell effects originate suddenly from the center point of the triad, without any apparent action by its members. In a single round, a False Keraptis can channel as many spells as he has groups of three subsumed minds, plus make a physical or magical attack of own. The head of the hierarchical mind can also see through the eyes of his vessels and cause them to move and act with minimal concentration.
For every ten subsumed minds under his control, a False Keraptis gains one additional level of experience and 1 Intelligence point. These benefits persist regardless of physical distance from his husks, so long as all remain alive and on the same plane with him. Though the death of an individual husk usually does not appreciably affect the hierarchical mind, the loss of several can cost a False Keraptis both levels and Intelligence.
Death
The death of a False Keraptis forces the hierarchical mind to make a successful saving throw vs. death magic as a wizard of its current level or instantly cease to exist. Success indicates that the hierarchical mind has 1 turn to reseat itself in a new body; if it cannot, it dies. The hierarchical mind can automatically assume control of any subsumed mind in its own infrastructure, so it preferentially selects the nearest one. If none are available, it can try to force its way into an imprinted (but not yet subsumed host), who must then make a successful saving throw vs. spell to resist. Should the hierarchical mind fail to reseat in its selected host, it can try for another on each subsequent round, until either it is successful or it dies. It cannot make a second attempt on any single host, however.
Successful reseating grants the hierarchical mind all the powers or benefits of its new body, though it loses those associated with the old one. Its spell-like abilities and “memories” remain intact, as do its connections with its remaining subsumed minds--in essence, the new host immediately ”becomes” the old False Keraptis.
The death of a hierarchical mind immediately releases all its subsumed minds, but does not restore the lost personalities, levels, or free will of those victims. Another False Keraptis can automatically add those subsumed minds to his own hierarchy by physically touching the husks; if that does not occur, the husks remain utterly devoid of mental capacity until retrained from scratch.