freyar
Extradimensional Explorer
For a little more progress (I guess I'm the only one interested in this monster
)...
The 3.5e blight clearly isn't what we want, unless the witness is a plant.
Not sure what the appropriate level spell should be (the current blight is 4th/5th level, depending on the spell list), but I'll choose doom because the flavor seems right.
Unnerving Fade (Su): When in stress (as determined by the DM, for example when wounded), there is a 1 in 6 chance per round (cumulative) that the possessed creature's features will fade. At the end of three rounds, the face will be completely blank. Anyone observing this fading is affected as if by a doom spell (CL 3rd, DC 18) (The DC is 10+1/2 HD + Cha modifier). The gebbeth has no control over this ability.

A Gebbeth has one particular 'ability' that is more terrifying than any other. In times of stress - when wounded, for example - there is a 1 in 6 chance that the creature's features will start to fade. The process takes 3 rounds in total, at the end of which the face will be completely blank. Anyone witnessing such a change should save vs spells or suffer the effects of a blight spell due to the unnerving prospect of an opponent's features altering without apparent reason.
The 3.5e blight clearly isn't what we want, unless the witness is a plant.

Unnerving Fade (Su): When in stress (as determined by the DM, for example when wounded), there is a 1 in 6 chance per round (cumulative) that the possessed creature's features will fade. At the end of three rounds, the face will be completely blank. Anyone observing this fading is affected as if by a doom spell (CL 3rd, DC 18) (The DC is 10+1/2 HD + Cha modifier). The gebbeth has no control over this ability.