The Collaborative International Dictionary of English v.0.48:

Rascally \Ras"cal*ly\ (r[a^]s"kal*l[y^]), a.
   Like a rascal; trickish or dishonest; base; worthless; --
   often in humorous disparagement, without implication of
   dishonesty.
   [1913 Webster]

         Our rascally porter is fallen fast asleep. --Swift.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rascally
    adj 1: playful in an appealingly bold way; "a roguish grin"
           [syn: devilish, rascally, roguish]
    2: lacking principles or scruples; "the rascally rabble"; "the
       tyranny of a scoundrelly aristocracy" - W.M. Thackaray; "the
       captain was set adrift by his roguish crew" [syn: rascally,
       roguish, scoundrelly, blackguardly]