impish
Playfully naughty in a fun, harmless way.
Impish means playfully mischievous, like a child who can't resist pulling harmless pranks or teasing others with a twinkle in their eye. An impish grin spreads across your face when you're planning something silly but not mean, like hiding your brother's shoe or sneaking an extra cookie when no one's looking.
Calling someone impish isn't really calling them devilish in a bad way. It captures that spark of fun-loving trouble that makes someone entertaining rather than annoying. An impish joke might make people laugh and shake their heads at the same time.
You might notice an impish quality in a friend who loves practical jokes, or see it in a story character who's always cooking up schemes that turn out mostly harmless. There's something lighthearted about being impish: the tricks are never cruel, just clever enough to get a reaction. When a teacher describes a student as having an impish sense of humor, it usually means that student keeps things interesting without crossing the line into real trouble.