Picture a garden. It's a sad space, neglected and filled with rubble, on the far side of Viva Piñata Island. It's here that the piñatas roam wild, their monochrome paper coverings denoting their feral nature. Hoist your shabby shovel, grow some grass and see if you can't make the area more hospitable to the local fauna.
Eventually, your little patch of land will start attracting piñatas - small ones like worms, grass snakes and sparrows. If they like the place, they'll move in, changing from boring black-and-white creatures to multicolored fiestas of papier-mâché plumage. The more piñatas you attract, the more successful your garden, but keep in mind that ol' circle of life: the grass snakes, for instance, might try to eat the worms, or at least scare them off. You'll need to create a harmonious living environment for all.