In case mimics, trappers, and lurker's above weren't enough disguised ambushers for your dungeons, I give you a window specific option.
https://mindweaverpg.wordpress.com/2021/05/19/biweekly-monster-fauxlight-add/
The party ended up getting a little sidetracked by a whole nest of ogres.
#playreport
https://mindweaverpg.wordpress.com/2023/06/30/play-report-kotb-barrier-march-session-52-surprise-ogres/
Searching for more information about the lay of the land around the bugbear crag, the party ends up ambushing a patrol, but when the ambush doesn't get surprise, the battle is far more even than intended.