As Bestiary 4 indicates, the soulbound shell is the soulbound mannequin recipe perfected, allowing even spellcasting abilities to make the transition. “Perfected,” that is, for a given value of perfected… After all, the wizard donating the soul dies in the process, and the spells he or she dies with are unalterably locked in the shell’s memory forever. As with lichdom, clones, retreat to the Astral Plane, and so many other attempts at longevity, a soulbound shell is at best a half-measure…and like most such measures, one that has the potential to go badly awry.
Masonix doesn't believe he is a construct. Something went wrong in the transfer of soulstuff (from a terminally ill donor), and the soulbound shell is convinced he is an actual wizard trapped within a marble body. By abusing loopholes in his instructions he engineered the death of his master, and he now studies ways to return to a flesh-and-blood body. Because Masonix does not understand his new state, he cannot comprehend why he is unable to change his spell roster. So after months of frustration he has decided to research the minds of other mages to figure out how they work… a process that involves more than a little abduction, humiliation, and dissection.
The Angelspan connects the Merchant Quarter and the Heights, where the aristocracy lives in manor houses that climb the hills with stately solemnity. Four statues grace each corner of the bridge, and at twilight they gleam in the setting sun more than they should. These are the Angels the span is named for, soulbound shells dedicated to guarding the moneyed elite from the consequences of their actions…particularly when those consequences involve upstart commoner heroes trying to sneak into the otherwise warded Heights after dark.
Dwarven arcane spellcasters are rare—so rare it is considered selfish for them to die without offering one last service to clan and thane. Thus many dwarven wizards and sorcerers on their deathbeds offer up their souls to be put into soulbound shells. If the shells lack some of the creativity the souls had in life, they make up for it in tirelessness, and a construct workshop led by a soulbound shell can turn out fine alloys, mechanical marvels, and even other constructs and clockworks at an inhuman (or indwarven) pace. Most dwarves do not realize, however, how susceptible these constructs are to mental manipulation…something the dwarves’ duergar enemies are adept at taking advantage of. Fully one soulbound shell in four in most dwarf cities ought to be considered compromised.
—Pathfinder Bestiary 4 249