WordNet sense 1 (ludicrously odd):

fantastic, fantastical, grotesque

WordNet sense 2 (being definitely out of the ordinary and unexpected; slightly odd or even a bit weird):

strange, unusual

WordNet sense 3 (a ludicrous or grotesque act done for fun and amusement):

caper, joke, prank, put-on, trick

WordNet sense 4 (act as or like a clown):

clown, clown around