Two friends, Raissa (voiced by Liza Soberano) and Jo (H.E.R.), discover a mysterious portal that transports them to the island of Nakali, an island in the Philippines inhabited by mythological creatures they have known since childhood through stories passed down in their families. There, they encounter various creatures, both friendly and dangerous. Among them are Manananggal (Lea Salonga), the most feared creature on the island, and Raww (Dave Franco), a weredog who becomes their friend. Jo and Raissa must find a way back home while facing various challenges along the way.

Focusing on Philippine mythology and folklore, the film involved hundreds of Filipino and American artists over a production period of approximately six years. Its hand-drawn 2D animation sequences were created by Snipple Animation Studios, an animation studio based in Quezon City, the Philippines. The Indonesian Film Censorship Institution (LSF) has classified Forgotten Island for audiences aged 13 and above. (anq)