Halloween only happens once a year, on October 31, and it does in Animal Crossing: New Horizons. When he arrives, Jack, the self-proclaimed reigning Halloween Czar, shows up on your island and asks you for some candy. Jack only shows up on the night of the event from 17:00 p.m. to midnight, so you need to talk to him quickly. Every time you give him candy he will reward you with a scary item. Yet his true desire is to receive lollipops from you, which is different from the traditional candies you receive from Nook's Cranny or other townspeople.
To receive lollipops, you must give your candies to candy lovers on your island. Cheaters will be other residents in costume, and they usually rush towards you during the event. They'll ask you to give them candies or play a prank on you, which usually requires them to change their appearance in some way. When you provide candy to them, they usually give you something in return. Sometimes it's a random item and other times it's a lollipop you want to bring back to Jack.
Lollipops are highly coveted by him, so you want to bring him as many as you can during the event. The more you do, the more special Halloween-themed items Jack hands you before the event ends at midnight. Whenever you run out of candies during the event, visit one of the houses with a resident inside and process them to then distribute them to cheaters wandering around. There's a lot of coming and going on your island, but Jack keeps his word to give you a variety of decorations.
