On April Fools’ Day Blanca will be wandering near your town plaza. Once you speak to her, Blanca will visit one of your villagers in his/her home and impersonate him/her.
Enter each villager’s home until you find one with two of the same villager inside (which means Blanca is there).
You can work out which villager is real and which is fake by listening to what the villagers say. The real villager will say his/her correct birthday, catchphrase or another piece of information.
If you’re unsure, you can continue to talk to the villagers to hear more information.
Once you have enough info to tell apart the real from the fake, say you know who the faker is and you’ll be given a towel. Present the towel to who you believe is the fake villager.
If you correctly gave Blanca the towel, then you will get a picture of the real villager .
Blanca will move from house to house after this point until you play her copycat game with all the villagers. At this point Blanca will return to the town plaza.
If you get all of your villager’s pictures, Blanca will be so impressed that she’ll send you a Pic of Blanca in the mail the next day.
If you’re not 100% confident about which villager is real or fake and desire Blanca’s picture, save before handing the towel, then reset the game if you chose the wrong option.
It’s "cheating", but nobody’s going to shout at you (except maybe Resetti).