whimsicality

(noun) the trait of acting unpredictably and more from whim or caprice than from reason or judgment. Synonyms: flightiness, arbitrariness, whimsy, whimsey, capriciousness. Example: "I despair at the flightiness and whimsicality of my memory."

(noun) the trait of behaving like an imp. Synonyms: impishness, mischievousness, puckishness.