Shade
Monster Junkie
I just remembered a place I saw something similar...your very own lock lurker conversion!
Here's what you gave it:
Partial Etherealness (Su): The stinger of the lock lurker exists wholly on the Ethereal plane. It can be materialized on the Material plane as a free action once per round, and returns to the Ethereal at the end of that round. Only creatures on the Material plane can attack the stinger, and only after the lock lurker has used a sting attack in a particular round. If the lock lurker is encountered on the Ethereal Plane, the entire creature will be visible and can be attacked. The stinger can always attack creatures on the Ethereal plane no matter where the lock lurker is.
Venom and food eaten are held in expandable body sacs on the Ethereal plane and brought to the Material plane as needed, in the same manner as the stinger.

Here's what you gave it:
Partial Etherealness (Su): The stinger of the lock lurker exists wholly on the Ethereal plane. It can be materialized on the Material plane as a free action once per round, and returns to the Ethereal at the end of that round. Only creatures on the Material plane can attack the stinger, and only after the lock lurker has used a sting attack in a particular round. If the lock lurker is encountered on the Ethereal Plane, the entire creature will be visible and can be attacked. The stinger can always attack creatures on the Ethereal plane no matter where the lock lurker is.
Venom and food eaten are held in expandable body sacs on the Ethereal plane and brought to the Material plane as needed, in the same manner as the stinger.