How comprehensive is total vision?

Question

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?

1. Creatures and objects that are squirreled away through the use of the skill Sleight of Hand or Hide, respectively.
2. Creatures and objects that are incorporeal.
3. Creatures and objects that are invisible or otherwise possess total concealment relative to the ethergaunt.
4. Creatures and objects that have total cover relative to the ethergaunt.
5. Creatures and objects that are present on a coterminous plane of existence like the Ethereal Plane and the Plane of Shadow
6. 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.

Answer 1

It's effectively "Super blindsight"

Although the ability can indeed defeat invisibility spells, it doesn't replicate see invisibility or true seeing. Instead, for most any instance that the ethergaunt would need to make a Spot check to notice a creature, it instead simply notices it. Even the darkstalker feat (Lords of Madness p179) should be ineffective, as the list of qualities it negates seems exhaustive ("blindsense, blindsight, scent, or tremorsense").

For Sleight-of-hand checks, spot checks oppose only the hiding of an object while observed. Thus an ethergaunt might indeed automatically notice an attempt to hide an object, but not an object already hidden, as that's a search check (those would have total cover anyway). It already notices all hidden creatures within range.

Incorporeal creatures and objects are not invisible due to incorporeality, but if an incorporeal creature were hidden inside an object large enough to give it total cover the ethergaunt couldn't spot it. However, if an incorporeal creature were merely invisible, its presence would be notable to the ethergaunt, as spot checks still apply in this case.

Total concealment would usually be negated, as (high) Spot checks can reveal the presence of most concealed creatures. Exactly like blindsight.

Total cover would not usually be negated, as there's no line of effect for this vision to function. It can't see through walls, because it doesn't say that it can; the only thing it can see through is its mask.

Neither blindsight nor a high spot check can see into the Ethereal or Shadow Planes, so the ethergaunt can't either. (Here is more information on etherealness, in addition to the Question's link)

Scrying sensors are objects, so the ethergaunt can see them within 40 feet.

Answer 2

total vision does exactly what it says it does: " discern all objects within 40 feet". If you put an ethergaunt in a 30x30 dungeon room, he can tell you how many worms are munching on the walls with 10 feet. Note that all of the ethergaunt's sensory organs are completely covered by a porcelain mask and total vision works "even through the mask" indicating that physical barriers are not going to impede the total vision ability.

Let's take the questions in order:

1. an ethergaunt will always spot a sleight of hand or hide attempt. Already hidden items can be noticed
2. Incorporeal creatures that have manifested would be noticed, "incorporeal beings have a tangible presence " but I would add only if they manifest would they be detectable
3. invisible /concealed characters will be spotted.
4. Total vision would seem to ignore concealment.

5. The creatures on the ethereal plane are invisible and incorporeal, and would not be noticed. (note that this presumes the ethergaunt is on the PMP and not its native ethereal plane)

6. Shadow planar creatures would be detected (per se) but as distance is warped on the plane of shadow there is no telling exactly how far away an observer is on the prime material plane. I think that the shadow plane detection would be subject to DM rule. There is no mention of the ability to influence other planes from within the plane of shadow.

7. Any creature with an Intelligence score of 12 or higher can notice the sensor by making a DC 20 Intelligence check, thus the scrying sensor would be detected.
8. prismatic wall/sphere only blocks the visible spectrum (its opaque). Since the Ethergaunt does not solely rely on vision, a character inside a prismatic sphere can be targeted/detected.

Sample spell lists are provided in the description