1. 
[syn: badly, mischievously, naughtily]
The Collaborative International Dictionary of English v.0.48:
Mischievous \Mis"chie*vous\ (m[i^]s"ch[-e]*v[u^]s), a.
   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.
   [1913 Webster]
         This false, wily, doubling disposition is intolerably
         mischievous to society.                  --South.
   [1913 Webster]
   Syn: Harmful; hurtful; detrimental; noxious; pernicious;
        destructive.
        [1913 Webster] -- Mis"chie*vous*ly, adv. --
        Mis"chie*vous*ness, n.
        [1913 Webster]
WordNet (r) 3.0 (2006):
mischievously
    adv 1: in a disobedient or naughty way; "he behaved badly in
           school"; "he mischievously looked for a chance to
           embarrass his sister"; "behaved naughtily when they had
           guests and was sent to his room" [syn: badly,
           mischievously, naughtily]