Before the big day, make a house for the Leprechauns. You may choose to make more of a friendly house to invite them to, or more of a trap.
Leprechauns love sugar cookies in the shape of shamrocks, with green sprinkles. Often they will leave behind gold coins as a thanks for the cookies. They are messy eaters so there are always cookie crumbs left behind.
Leprechauns are quite mischievous guests. They often leave behind green footprints, turn things in the house upside down, and even forget to flush their green pee down the toilet!