An ethergaunt possesses the extraordinary ability total vision that says
An ethergaunt's superdeveloped brain and countless facial sensory organs allow it to discern all objects within 40 feet, even through the mask that hides its face. An ethergaunt usually does not need to make Spot or Listen checks to notice creatures within range of its total vision. A silence spell has no bearing upon an ethergaunt's total vision. (Fiend Folio 65)
(Link added.) At a distance of 40 ft., does an ethergaunt's special ability total vision allow the ethergaunt to detect the following creatures and objects?
- Creatures and objects that are squirreled away through the use of the skill Sleight of Hand or Hide, respectively.
- Creatures and objects that are incorporeal.
- Creatures and objects that are invisible or otherwise possess total concealment relative to the ethergaunt.
- Creatures and objects that have total cover relative to the ethergaunt.
- Creatures and objects that are present on a coterminous plane of existence like the Ethereal Plane and the Plane of Shadow
- Magically created effects like scrying sensors and the effect of the 9th-level Sor/Wiz spell prismatic sphere [evoc] (PH 264).
I assume that an ethergaunt's special ability total vision already includes penetrating up to 40 ft. of mundane and magical darkness, fog, and smoke as well as weather effects, but—especially if I'm mistaken—an answer may want to addresses such effects separately.
Note: Ethergaunts cast spells as wizards do, but I'm trying to figure out exactly what spells ethergaunts should prepare. If its special ability total vision is capable of seeing invisible and hidden creatures, for instance, this frees up a couple of valuable spell slots.