Nightwings - giant flying shadow-bats.
Nightshades (nightwalkers, nightwings, and nightcrawlers) were a package deal in the Rules Cyclopedia and 3E Monster Manuals, but nightwalkers became a solo act in 4E and 5E. Shame.Now I am reminded of Nightwalkers and really need me some of those!
Not quite a core monster, since they only appeared in the Immortals Rules (which didn't make it into the Rules Cyclopedia). But there are a number of really interesting and unusual monsters in there, to be sure...Tonals - giant sentient soap bubbles of pure arcane energy.
How could I get forget the thoul in my list?? One hopes they'll eventually return in a first-party product.The Goodman Games B1/B2 update has the Thoul! Just got to use one for the first time in ages last week.