From Nookipedia, the Animal Crossing wiki
(Redirected from U.F.O)
The U.F.O. is a disc-like object that flies over the player's town on one random weekday, between 6 a.m. and 6 a.m. the next day. Gulliver, the captain of the U.F.O., calls it the Porpoise 5000, which is a reference to Captain Olimar's ship in the Pikmin games, the S.S. Dolphin, both of which are named after types of sea mammal that are closely related. It appears only in Animal Crossing: Wild World and Animal Crossing: City Folk.
In Animal Crossing: Wild World, Gulliver's U.F.O. appears on a random weekday on the top screen between 6 a.m. and 6 a.m. when the final digit of the time is a 2 or 7 the next day, while no other special visitor is in town.. If shot down with a slingshot, it will crash, together with an unconscious Gulliver, on a signpost in town. This will cause five U.F.O. parts to scatter around town. If the player returns them all to Gulliver before 6 a.m., he will reward him or her with one of his rare items.
The U.F.O. plays a similar role in Animal Crossing: City Folk as it does in Animal Crossing: Wild World, but after being shot down with a slingshot, it does not immediately crash and instead appears crashed the next day on the beach. One 'UFO part' (NTSC) or 'spaceship part' (PAL) can be found on the ground somewhere in town after the player hits the U.F.O.. Like in Animal Crossing: Wild World, returning the part to Gulliver will result in a rare item being awarded.
In this game, the U.F.O. appears only during the first ten minutes of an hour and enters town when the final digit of the time hits 2 or 7. It always flies on the top row of the 2nd, 3rd or 4th acres from the top of town, which is the same path that the balloons take.
 Gulliver's items