The Collaborative International Dictionary of English v.0.48:

Prankish \Prank"ish\, a.
   Full of pranks; frolicsome.
   [1913 Webster]

WordNet (r) 3.0 (2006):

prankish
    adj 1: naughtily or annoyingly playful; "teasing and worrying
           with impish laughter"; "a wicked prank" [syn: arch,
           impish, implike, mischievous, pixilated,
           prankish, puckish, wicked]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "prankish":
   arch, devilish, elfish, elvish, foolish, full of mischief,
   high-spirited, impish, knavish, mischief-loving, mischievous,
   playful, pranksome, pranky, puckish, roguish, scampish, scapegrace,
   sportive, trickish, tricksy, tricky, waggish