From Wikipedia:
The player's objective in the game is to track down Pinkie Pie's presents and puzzle pieces hidden throughout Ponyville.[3] As Pinkie Pie, the player navigates throughout the entire town looking for the puzzle pieces and gifts while interacting with other ponies. The top part of the Nintendo DS's screen acts as a map, with the puzzle pieces and gifts located in certain areas. The player can also save its progress throughout the game.
Similar to Crystal Princess: The Runaway Rainbow, the game also features puzzles and mini-games utilizing the Nintendo DS's capabilities.