Majora's Mask is the direct sequel to the 1998 mega-hit The Legend of Zelda: Ocarina of Time. After Link saves Hyrule and returns back to the past to become child link once again, he goes in search of his fairy from Ocarina of Time, Navi. While searching in the forest, he is transported to a parallel world of Hyrule called Termina. He once again finds himself in position to save the world. The moon of Termina is on a collision course with the ground and will destroy Termina if it occurs. Your job is to find a way to stop the moon from falling. The catch is you only have 72 hours (3 days) in which to do it.
You must travel to the four lands of Termina and battle through the dungeons there to save the land. You will aquire many masks to help you with the feat. The way you are able to do all this in the 3 day time limit is that you are able to warp back in time to the beginning of the first day anytime that you want. As long as you do it before the moon hits, you will be safe for another 72 hours. However, when you warp back, everything in the world will be reset, including the dungeons. All your non-essential items (bombs, arrows, rupees, etc...) will be dropped to zero and all of the characters will start their 3-day routines over again.
For more information see the Wikipedia page at the following link: en.wikipedia.org/wiki/The_Legend_of_Zelda:_Majora%27s_Mask