Synonyms for Imp (same or very similar meaning)
WordNet sense 1 (one who is playfully mischievous):
monkey, rapscallion, rascal, scalawag, scamp, scallywagWordNet sense 2 ((folklore) fairies that are somewhat mischievous):
brownie, elf, gremlin, hob, pixie, pixyFrom the ODE community, based on WordNetadd/edit