The suggestions for this prompt were funerals, reading of a will, business meetings and family portraits. For a serious occasions I think I would just go for a black cream, Barry M Black Forest or Orly Liquid Vinyl.
Halloween polishes I like from my collection would be things such as Heists are Dumb from Prism Polish which glows in the dark. Another would be Evil Pumpkin from Fancy Gloss which is a typical orange base with different sized black hex glitters.