I'm more excited by story than by mechanics, so a monster that properly evokes the legends and myth of the monster is much more exciting to me than a bucket o' stats. The Will O' Wisp hasn't done that very well, historically, and it's exciting to see it get its just deserts. It works better than, say, something like the Succubus, whose charm only lasts a few moments, and better than something like the Abyssal Ghoul, which seems to lack a justification to exist.
They're from the Minis HB. A quick google will get you an old excerpt with the stats. Basic gibbering abomination.

From the 3.5 Miniatures Handbook Art Gallery.
There were many weird, frankly tractionless monsters in that book. OTOH, it also had Kruthiks, which are quickly becoming one of my favorite monsters!
