Solusek B (Nagefen's Lair) is flagged See Invisible as a dungeon. Every
single monster there can see invisible. In Lower Guk, Undead Frogs can now
see through Bard invis. Spiders and bats cannot, and neither can the live
frogluks. I am not sure whether Greater Iced Bones can or not, but I would
recommend having your cleric invis you to Undead.

The undead froggies could not see through bard invis last patch and it was
changed.The Undead in Unrest still cannot however. One good thing about Bard
invis in Unrest is that neither the living things (tentacle terrors, fungus)
or the dead things (skeles and hags) can see through our invis. Anyone else
needs both invis and invis to undead, and a quick prayer that neither wear
off to fast, since I don't believe any class has both. Yay bards.

Two things about bard invis - the higher you get, the less it blinks. I'd
say mine has blinked maybe once in the last 4 hours of use (now at 195
skill). Secondly, remember that if you go into auto-attack mode you
immediately become visible, so be careful when you are typing (ever try to
talk to an NPC and accidentally auto-attack him? I have).

Ariell Thunderwolf, Karana