All 4 Uses of

mischievous
in
War and Peace

It was obviously strange to her to think that this stern handsome man should be Andrusha—the slender mischievous boy who had been her playfellow in childhood.
Chpt 1 *

mischievous = tending toward playful misbehavior

Petya was a big handsome boy of thirteen, merry, witty, and mischievous, with a voice that was already breaking.†
Chpt 7

Natasha suddenly said with a mischievous smile such as Princess Mary had not seen on her face for a long time, "he has somehow grown so clean, smooth, and fresh—as if he had just come out of a Russian bath; do you understand?†
Chpt 15

And the same mischievous smile lingered for a long time on her face as if it had been forgotten there.†
Chpt 15

Definitions:

(1) (mischievous)
playfully causing minor trouble; or describing the smile of someone doing so

Much less commonly, mischievous can reference real harm without any sense of fun. But in modern writing, that usage has largely shifted to other words like malicious, destructive, or damaging.
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

In law, mischievous references a property crime such as vandalism or graffiti. Very rarely, the word can reference someone or something causing serious damage.

In archaic literature mischievous often refers to bad behavior without any connotation of playfulness or of the harm being minor.