Short answers, pulled from the story.
The cartridge contained save data belonging to a twelve-year-old boy named Ben who had drowned eight years prior. This cursed object triggered a multimedia horror phenomenon known as Ben Drowned that broke the game's reality and left Link alone in Clock Town with all inhabitants vanished.
Ben was a member of the Moon Children cult who was sacrificed alongside several other individuals under the pretense of achieving ascension. His spirit became known as BEN and eventually contacted Jadusable through the game and his computer to spread his influence across the internet.
The third arc Awakening began on the 17th of March 2020 and concluded on the 31st of October 2020. This arc coincided with the 20th anniversary of The Legend of Zelda: Majora's Mask and was split into two parts called Methods of Revolution and The Last Hero.
The Eternity Project is a series of servers that house the digital consciousnesses of humans who opted to escape the distress of the real world by permanently uploading themselves to live in virtual game worlds. The Majora's Mask world was a failed beta test of this project that became hopelessly corrupted and broken.
Ben Drowned laid groundwork for other video-game-themed horror narratives such as Herobrine from Minecraft and influenced independent and analog horror shorts. Media scholars describe it as a landmark in modern urban mythology that explores digital uncanny and internet-age anxieties about technological vulnerability.