First of all, you should design a shape that is particularly funny, but also attracts attention, especially the shape of the spider in the picture below. It looks really scary and cute.
Then look like a handsome magician. Make a black robe with gold lettering, a pointed hat, and a jack-o-lantern.
Then there is the girl's styling. The girl wears a black dress and wears a big felt hat. It feels cool, so let's design this one!
Then dress up as a cute monster costume. Monster costumes can be made according to their own imagination, and can also be purchased online.
Then there is the black hat and robes, which looks more suitable for Halloween. You can make a cloak with a black cloth, and the hat needs to be purchased.