what do you know.

how is this for a start (will compare to the glimmerskin later)
A vagabond is a solitary, enigmatic creature of an inexplicable nature. This creature exists as a disembodied life force with the ability to inhabit any physical form. The true nature and origin of the vagabonds is a mystery, but they seem to be most often found on the Material Plane.
A vagabond has a powerful mentality (Int 20, Wis X, Cha X), though its incorporeal form provides limited means at best of interacting with the physical world. It has an array of psionic powers, though it cannot make use of these unless it has a body. A vagabond is immune to non-psionic mind-affecting effects, and while incorporeal is immune to any attacks from a corporeal source. A vagabond will wander alone until it finds a suitable form to exist as. Vagabonds can detect each other up to a mile away, and will avoid each other if possible.
A vagabond is neutral in alignment until it takes on another form. It can accomplish this in one of three ways. The first way is to form a corporeal body from (nothing? Air? Matter?), starting as a small inky blob on the ground that quickly enlarges into three dimensions, fills out, and forms finer details. The second method is to find a fresh corpse, which the vagabond enters and controls, restoring the body to full health. Lastly, a vagabond can inhabit a willing living creature. Regardless, the form chosen must have an Intelligence score, and once a vagabond chooses its form it is locked into that form and cannot leave (except through the use of psionics). The vagabond gains all the abilities of the form it has chosen (except Su and Sp?), but has access to none of the memories or skills of the creature. Vagabonds are thus typically very inquisitive, even about mundane or personal details. They will willingly accompany intelligent creatures, and relish the opportunity to do so. If the body a vagabond inhabits is slain, the vagabond’s incorporeal form will depart and never return to that area.