April Fool's Day
From Nookipedia, the Animal Crossing wiki
 In Animal Crossing
In Animal Crossing, Tortimer gives the player his prized software Super Tortimer, which is actually a fake NES Game. While, most other characters and villagers will try to trick the player when first spoken to, with varying degrees of finesse. Some villagers will tend to send messages with some pranks.
 In Wild World
 In City Folk
In Animal Crossing: City Folk, the player receives nothing from Tortimer. After his saying he is not keen on April Fools, he will give the player a furniture leaf, which resembles the furniture leaf which can be found on the ground outside in the town. It does not turn into furniture when placed inside a house, however, but is an item of furniture itself.
 In New Leaf
The April Fool's Day varies in New Leaf compared to its appearance in other games. The villagers will also try to trick the player. Blanca is the special character that visits the player's town during April Fool's Day, and can be found next to the Town Tree in the Event Plaza. If the player speaks to Blanca, she will inform them about April Fool's Day, stating that she wants to create a game to play with them. The game consists of the player finding Blanca in one of the villager's homes, in which she will take the appearance of the villager whose home she is in. You must identify her from the real villagers and her. The player will be able to identify through the statements the villagers say whether Blanca or the real villagers.
When the player decided to identify by talking to villagers, the speaking villager will give the player a towel, and must go to the villager they think is Blanca so that they can wipe their face, to remove make-up. When talking to the assumed Blanca, the player will give them the towel. The villager will turn around and rub their face, turning around to reveal their true identity. If it's Blanca, there will be a poof of smoke and she will reveal herself. The real villager will be relieved, knowing the player knows enough about them. Blanca will disappear to another villager's house and the villager that was helped will give the player a picture. If it's not Blanca, she will disappear to another villager's house. If Blanca is busted each time she will give her picture.