Matango

Matango, known in the US as Attack of the Mushroom People, is a Japanese psychological horror film from the director and special effects director of the original Godzilla. It's an adaptation of a short story called "The Voice in the Night" by William Hope Hodgson.

When a Japanese yacht is damaged in a storm, its crew and passengers make their way to a nearby island. The island is apparently deserted, though the castaways soon discover a beached research ship on the other side of the island. An examination of the ship, the insides of which are encrusted with a thick mold, soon reveals that it had an international crew which appear to be involved in radiation and fallout research. Despite this it seems that the crew survived for some time after the ship was beached, however there is no indication of their current whereabouts.

Although mushrooms are unusually plentiful on the island, the ship's captain warns the passengers not to eat them because of the danger of poisoning, and to concentrate on birds and turtle eggs. However, it is soon discovered that birds are afraid of the island and that turtle eggs are scarce. A small supply of canned food is found on the research ship, but this only buys the crew some time. Inevitably, members of the crew begin eating the mushrooms. In the meantime, they also discover that the crew of the abandoned ship may not have vanished as completely as they'd originally thought...

Tropes used in Matango include:

Adaptation Expansion: Very much so. For one thing, the castaways never turn on each other in the original story though that really doesn't make the short story's ending any happier than the movie's.
Body Horror: So much body horror.
Cosmic Horror: The mushrooms and their effects could be a low-eye version.
Does This Remind You of Anything?: A lot of people got worked up over the effects, because they looked like radiation burns. The movie could be a metaphor for the dangers of fallout. Sure the food looks unharmed but...
Face Heel Turn: Where do we even begin?
Festering Fungus: And how.
Foreshadowing: In the beginning everyone goes on about how great and trusting they are to each other.
Fungus Humongous
It Got Worse: Starting with a damaged ship...then the island...then all those mushrooms are actually dangerous...no birds or fish...well shit!
I Love Nuclear Power: The mushrooms may or may not have been mutated by the radiation experiments conducted by the research vessel.
Mind Screw: The film never makes it clear whether the mushrooms really turned people into monsters or if they were simply illusions.
- Although we do see the narrator's face mutating at the end of the film.
Mushroom Man: Trope namer
Recycled in Space: Theme-wise it's something of Night of the Living Dead...on an island! Where they should fear each other more than the mushrooms.
- This troper can't recall where it is now, but there was a B-movie reviewer who actually compared the film to Gilligan's Island... In a Horror Film!
Teacher-Student Romance: Kenji is a college professor while Akiko is a student of his. They were ultimately seperated, and Kenji laments having left the island to stay with her.