According to the yochlol description (MM p. 65), it's a shapechanger that can transform into the form of a female drow.
According to all the Elves: Drow statblocks (MM p. 128-129), drow are all affected by sunlight.
In my adventure, the characters are attacked by poisonous spiders. One spider remains in the back watching. When the battle is near the end that spider leaves to reappear later as a female drow.
I'm wondering whether the sunlight would affect a demon and most specifically yochlol whatever its current form. My idea is that if one of the characters is a drow, that character can eventually notice that specific glitch. A regular elf may also notice, but with a higher perception DC. Other characters can't notice without specifically rolling a perception which is rather unlikely to happen.
