WordNet (r) 3.0 (2006):

gremlin
    n 1: (folklore) fairies that are somewhat mischievous [syn:
         elf, hob, gremlin, pixie, pixy, brownie, imp]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "gremlin":
   Ariel, Befind, Corrigan, Dingbelle, Fifinella, Finnbeara, Hob,
   Hobgoblin, Mab, Oberon, Puck, Titania, bad fairy, bad peri,
   banshee, brownie, cluricaune, deviling, devilkin, diablotin, dwarf,
   elf, erlking, fairy, fairy queen, fay, gnome, goblin, hob, imp,
   kobold, leprechaun, little devil, ouphe, peri, pixie, poltergeist,
   pooka, puca, puck, pwca, sprite, sylph, sylphid, tokoloshe,
   young devil