WordNet (r) 3.0 (2006):

prankster
    n 1: someone who plays practical jokes on others [syn:
         prankster, cut-up, trickster, tricker, hoaxer,
         practical joker]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "prankster":
   bad boy, banana, booger, buffoon, bugger, burlesquer, caricaturist,
   clown, comedian, comic, cutup, devil, elf, enfant terrible,
   epigrammatist, funmaker, funnyman, gag writer, gagman, gagster,
   hood, hoodlum, hooligan, humorist, imp, ironist, jester, joker,
   jokesmith, jokester, knave, lampooner, little devil, little monkey,
   little rascal, madcap, minx, mischief, mischief-maker, parodist,
   pixie, practical joker, puck, punner, punster, quipster,
   rapscallion, rascal, reparteeist, rogue, rowdy, ruffian, satirist,
   scamp, scapegrace, wag, wagwit, wisecracker, wit, witling, zany