The ghost that appears at night in Animal Crossing is Wisp.
Wisp is a recurring ghost character in the Animal Crossing series. In Animal Crossing: New Horizons, he can appear randomly after nightfall, usually floating around the island in a frightened state. When the player approaches him, he becomes startled and breaks apart into five glowing spirit pieces.
The player must search the island with a net to collect the scattered pieces and return them to Wisp. In exchange, Wisp offers either something new or something the player does not already own. This makes him a small nighttime event as well as a source of occasional furniture, clothing, or other rewards.
Wisp is easy to confuse with other wandering characters, but Pascal is an otter associated with scallops, Gulliver is a shipwrecked seagull, and Blanca is a cat known for disguise-related events. Wisp is the series’ unmistakable ghostly visitor.