The phrase "HAPPY HALLOWEEN" is surrounded by jack-o'-lanterns, bats, spiders, cobwebs, candy, and a full moon.
The full moon on Halloween is often associated with increased werewolf activity in folklore, though there's no scientific evidence to support this belief.
Try using orange and black for the jack-o'-lanterns and bats, and purple or dark blue for the cobwebs and moon to create a spooky atmosphere.