How to spot a sneaky character that uses Hide in Plain sight + leaves no trace + has high "hide" ability

Question

I see this question as the continuation to a previous question (best-ways-to-spot-sneaky-characters).

What are all the possible ways to spot an NPC or a player that has Hide in Plain sight (HiPs), does not emit any sound nor leaves any feet trace (e.g. is incorporeal), and has a very high hide ability score?

In our specific case: At level 30 the rogue in our party has Hide in Plain sight (HiPs); when she hides without moving her bonus is minimum 107 = skill 66 (basic, Des, and armor with the bonus shadow +15), +20 or +40 (if she has superior invisibility casted on herself, as per Spell Compendium page 125) + 1d20. In addition to this, if in need, she can increase her hide check up to +20ish, draining her life essence from her shadow form (Perfect Wight supernatural ability).

We understand (please correct me if wrong) that the rogue maintains her hide while attacking either from melee or distance (although she needs to roll it after every attack), so basically enemies never have line of sight over her when she attacks. Also she has been casting spells with scrolls claiming this would not hinder her hide condition, again no line of sight.

PS. I am good friends with the all the players in the party, the player that uses HiPs has been using this strategy for years in our game, and I can recall very few instances in which an enemy was able to spot her (I bet that these were less than five). So I am simply curious to know more, also because they are facing epic enemies that may know some “tricks” that I am not aware of.

I have tried to answer to this question below, nonetheless I wonder if some of my answers may not be correct.

Answer 1

Here are some possibilities that I have found from other similar questions, most from the answer of Brian Ballun Stanton to the question how to spot sneaky characters

FEATS

1. Earth sense - Note: I believe in this case it would not work as incorporeals do not touch the ground.
2. Mindsight + mindbender

ITEMS:

1. the ever so useful bag of flour
2. There is a staff somewhere that allows the holder to spot enemies in the area, but I cannot remember the name of it.
3. The ring of X ray vision (Dungeon Master) - Note: in regards to this we are still not sure.

SPELLS Boost the spot check with:

1. Divine Insight (paladin/cleric), MAX+15 (Spell Compendium page 50)
2. Improvisation (bard) MAX+7 (Spell Compendium page 50)

Note: in this specific scenario this boost would not be enough to spot the rogue.

Boosting the "spot" ability (as discussed in this question) Note: unfortunately, in Hey I can Chan's answer to the question most of the objects that give a high bonus are in sources that we do not use. We don't use any ambientation, MIC, Tome of Magic, Tome of Battle, nor magazines.

Blindsight (Spell Compendium page 32) -

Note: I believe this would only work if the rogue comes close to the target as it is 30 feet, or otherwise the person casts blindsight on himself and starts running around the area to find the rogue.

Alarm (Player Handbook) -

Note: this would work only if the rogue comes close to the area (20 ft radius) where the spell is, this only informs the caster of the presence, does not indicate where. Thus needs another spell (e.g. extended glitterdust?, corpse candle?)

Corpse candle (Spell Compendium page 53) -

Note: this is only 5 feet radius, but can be moved around. It may be very helpful to find a rogue that is close. I guess it is impossible to use this to find a rogue sneak attacking from the distance.

Faerie Fire (Player Handbook page 229) - Note: this is only 5 feet radius, has a longer range compared to Corpse candle, but I cannot see how this could work even if you prepared the action to cast this spell as soon as you see an arrow being thrown at you (or an ally).

Glitterdust (Player Handbook) - Note: probably helpful, if you were able to predict where the rogue would be (10 ft radius). Maybe to be kept in preparation ?

Detect spells

1. Detect Magic
2. Detect Alignment
3. Detect thoughts

Note: these are cones of 60 ft. would work in case the rogue is close to the target and the target looks around themselves, or otherwise the person casts blindsight on himself and starts running around the area to find the rogue. I any case before they knew where the rogue is they would probably die as it takes 3 rounds to work.

SPELLS that would not work (based on previous questions):

Arcane sight – as there is no line of sight. True seeing – as the player is not invisible. In regards to this we agree with the player that enemies and allies that have "True Seeing" nullify her +40 hide due to being invisible. Darkvision – same as above. Any kind of light, as it would only create more shadows.

CONTINGENCY SPELLS (although I never made a list of which spell could be actually good in this scenario, and not much comes to mind)

1. Otiluke’s resilient sphere on the self, to activate when hit (but again this helps to survive, not to spot the rogue). Would need a second contingency based on one of the spells above (e.g. glitterdust?).

PREPARATION ACTIONS:

1. If the enemy of the rogue were a fighter. the fighter could try to grapple when hit (if in melee), I cannot see any chance for the fighter to find a rogue hiding and attacking from the distance.

2. The target could decide to try spotting the dart or arrow when they are shot (would this need a normal spot vs hide check or would be automatic spot?)

Answer 2

Most of the abilities that would detect this creature are negated by one vague line in the Incorporeal Subtype.

Nonvisual senses, such as scent and blindsight, are either ineffective or only partly effective with regard to incorporeal creatures.

If you read that to mean that they are all entirely ineffective, then senses such as Lifesense or Mindsight or Touchsight that would normally automatically find a hidden rogue do not.

What you are left with is True Seeing (to lower the DC) + Spot Checks.

I vaguely recall some specific spells (in Ghostwalk or Libris Mortis, perhaps?) that detect Incorporeal creatures specifically. Those would potentially be of use.

Otherwise the Rogue does not appear to be immune to divinations, meaning a number of spells starting with the 4th-level Locate Creature can detect their direction, square, or other information about them enabling a typical wizard to pop time stop and set up the world's most horrendous deathtrap around that location then wrap the whole thing in a forcecage and teleport the entire cage and its contents to the plane of fire.