The quality of being playfully naughty is mischievousness. I wouldn't put your sister in charge of the balloons for the party — her mischievousness might result in a water balloon attack later!
A rascally child and a practical joker are both known for their mischievousness. Calling someone on the phone to ask if their refrigerator is running doesn't demonstrate your originality — but it does highlight your mischievousness! Think of it as a tendency to make mischief, which is often slightly funny, frequently annoying, and usually harmless.