April Fools' Day is a special event in Animal Crossing: New Leaf that takes place on April 1. On this day, you can meet Blanca in the town square. Blanca will go to your villagers' houses one by one and pretend to be each villager. If you figure out which of the two is the impostor, you get your villager's picture.
To start the guessing game, you have to first find Blanca, who is walking around the town square area. Unlike other special visitors, Blanca does not stand still near the town tree, so be sure to walk around the area until you find Blanca.
After you talk to Blanca, the cat will disappear. Now you have to visit each of your villagers in his or her house. You can tell if a villager is at home by looking for smoke from the chimney. Go into each villagers' house until you find a house where there are two villagers in the same house. One of the two is a fake. Talk to one of them and he/she will ask you to figure out which one of them is the fake.
Listen carefully to what each villager says. Each one will say some identifying information, such as his or her birthday, favorite saying, dream for the future, or birth order and number of siblings. Whichever villager says incorrect information is the fake.
After each villager speaks, the villager will ask if you have figure out which of them is the fake. If you don't know, just say that you don't know, and you can talk to them again to get more information.
If you have figured it out, tell the villager that you figured it out. The villager will give you a face towel. Talk to the FAKE and give the towel to the fake. The villager will use the face towel, and if you were correct, the fake will turn into Blanca. Blanca disappears, and the real villager gives you his or her picture.
Blanca will go to each villager's house one by one. Just go around looking for the house that has two of the same villager in it and play the guessing game, using villager information to determine which is the fake. After you have played the game with all the villagers, Blanca will go back to the town square.
If you get the correct answers and get all the villagers' pictures, you will receive Blanca's picture in the mail the next day.