If you know someone who's playful and mischievous, you can describe them as impish. Your impish little brother probably gets away with all kinds of pranks because he's so cute.
If you're impish, you might play practical jokes on people, tease them, tickle them, or be otherwise cheerfully annoying. The troublemaker in a kindergarten class is likely to be fairly impish, naughty and a little silly. The adjective impish comes from imp, a mythological creature that's similar to a fairy but known in folklore for its jokes and pranks.