mischievous

mischievous is an   Adverb

Definition:

[1] Causing mischief; harmful; hurtful; -- now often applied where the evil is done carelessly or in sport; as, a mischievous child. "Most mischievous foul sin." Shak. This false, wily, doubling disposition is intolerably mischievous to society. South.

Synonyms: