All 6 Uses

mischievous
in
The Wedding, by Nicholas Sparks
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Then, with a mischievous grin: "Could be worse, though, too."†
Chpt 1 *
Though his expression remained serious as he spoke, I detected the mischievous gleam in his eye.†
Chpt 4
His smiled mischievously.†
Chpt 9

mischievously = in a manner that playfully causes minor trouble
Her eyes were mischievous.†
Chpt 16
In the darkness, I could just make out her mischievous expression, as if she were simultaneously scandalized and thrilled by what had happened.†
Chpt 16
He cut me off with a mischievous grin.†
Chpt 18

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)
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.