In my Britannia 3E campaign, I'm using a bunch of stuff from Oriental Adventures (long story). In particular, I'm using the spell lists, and the spirit subtype for certain creatures, including outsiders and dragons.
Last session, the party fought a very young red dragon. They were getting beaten up (naturally), and the druid cast invisibility to spirits. Here's the abbreviated spell description from OA:
Abjuration
Level: Sha 2
Target: 1 touched creature/level
Duration: 10 mins/level (D)
Save: Will negates
SR: Yes (harmless)
If a spirit fails its saving throw, it can't perceive the warded creatures and acts as though the warded creatures are not there. The warded creatures can move freely among spirits without being noticed, although they are perfectly visible to all other types of creatures. If a warded creature touches or attacks a spirit (even with a spell), the spell ends for all recipients.
Question: would the dragon's blindsight help against this spell? Would it even be able to do anything against the warded creatures if it failed the save?
I ruled that the dragon couldn't see or perceive the warded creatures even with blindsight, but it was still aware that they were there. So it couldn't finish off the severely wounded berserker in melee, but it did fry them nicely with its breath weapon.
I'd be interested to know how others would have run it.
Last session, the party fought a very young red dragon. They were getting beaten up (naturally), and the druid cast invisibility to spirits. Here's the abbreviated spell description from OA:
Abjuration
Level: Sha 2
Target: 1 touched creature/level
Duration: 10 mins/level (D)
Save: Will negates
SR: Yes (harmless)
If a spirit fails its saving throw, it can't perceive the warded creatures and acts as though the warded creatures are not there. The warded creatures can move freely among spirits without being noticed, although they are perfectly visible to all other types of creatures. If a warded creature touches or attacks a spirit (even with a spell), the spell ends for all recipients.
Question: would the dragon's blindsight help against this spell? Would it even be able to do anything against the warded creatures if it failed the save?
I ruled that the dragon couldn't see or perceive the warded creatures even with blindsight, but it was still aware that they were there. So it couldn't finish off the severely wounded berserker in melee, but it did fry them nicely with its breath weapon.

I'd be interested to know how others would have run it.