The Legend of Zelda: A Link Between Worlds contains a variety of collectible items, including Maiamais. These harmless creatures were somehow scattered throughout the game, and you're free to go in search of them all. Before doing that, you must obtain bombs from Ravio and then use the explosives to blow up the entrance of a cave to the east of Link’s house, the one warning travelers of a dangerous creature.
As it turns out, Mother Maiamai is quite peaceful and worried about her kids. In fact, she gives Link the Maiamai Map that shows the location of all 100 lost Maiamais. Finding the buggers will be tricky. You'll need to utilize Link's merging ability to travel along walls and across chasms. That said, we'll make it much easier tracking them down. On that note, here are the best ways to find the lost Maiamais.
For more info, check out Prima's A Link Between Worlds eGuide.