Matango is a motile form of toxic mushroom that when devoured infects the consumer with its spores. Eventually the consumer becomes infected to the point that they literally become a horrific Matango themselves.
While not technically an actual kaiju or a mutation for that matter, it is the infection of the spores creating "Mushroom People" that makes the Matango such a monstrous lifeform.
So far Matango's first and only film appearance was in it's 1963 self titled film directed by the legendary Ishiro Honda. In the film the group of sailors become stranded on an island in the south pacific that is greatly populated by the Matango. Food on the island is incredibly hard to come by to the point that eventually, despite knowing the danger, the crew succumbs to the temptation offered by the mushrooms to the point that they all become Matango themselves.
The film differentiated in many ways from the traditional kaiju movies of the showa era in that for one, the Matango were not a form of mutation or alien. Secondly, the film served as more of a survival/horror movie rather than your usual sci-fi/monster flick. The make up effects in the film also briefly almost prevented the release of the movie at one point due to the fact that the moments in the transformation of the characters into the Matango bared striking resemblances to people irradiated by nuclear fallout following the Hiroshima and Nagasaki bombings.
Other Appearances in Media
Outside of its only film appearance the Matango has made an appearance in the NES game Godzilla Monster of Monsters. In the game the Matango appear in their own "Sub-Space" levels in which the player, controlling Godzilla or Mothra, must destroy a Matango hive (coming in three different levels of difficulty) in order to clear the level. While trying to destroy the hive the player must also contend with projectile spores and even smaller individual floating Matango.
The Matango appear in various forms. All of which begin with the actual mushroom forms. In the mushroom form the Matango appear as nothing more than your average mushroom ranging in size from small 2 inch tall individuals to mushrooms a little over a foot tall. Normally they appear in very large clusters or hives. It is in their small sizes where the Matango are actually in their most dangerous forms due to their edibility. This becomes a deadly trait to any starving organisms coming across them. When devoured, the organisms are then infected with the spores which gradually take over their host.
First Level Of Infection
In this first stage of infection the victim appears almost completely normal. At the most their skin might seem dark around the eyes and their lips may be dry. The most significant change is in their personality. Victims usually become more violent towards others, suffer hallucinations, and even somewhat pressuring those around them to consume the Matango also.
Second Level Of Infection
The second level is where the most dramatic change takes place mentally. The host is no longer their former self and is fully under the influence of the Matango. It is under this influence where the host also becomes most dangerous to those around them in their ability to manipulate their companions into eating Matango. Also on several areas of their body there are break outs of mushroom like ulcers, this happens mostly around the arms, face, and scalp area.
Third Level Of Infection
In the third level the mushroom like ulcers fully cover the hosts body. Fingers start to become fused together and the ability to produce vocal sounds is reduced to nothing more than moans or grunts. Their motor skills are reduced to a far more sluggish and lumbering motion.
Fourth and Final Level Of Infection
The final level of infection is where the host has almost fully taken the traditional umbrella-top, mushroom form. Still possessing arms and legs but no faces or any other features the host had prior to the infection. It is these forms are what gave those infected by the Matango the nickname "Mushroom People." With no vocal capabilities and moving at slow speeds, these forms rely purely on stealth and ambush when on the attack. Aside from the other forms this form very rarely ventures outside of the hive.
Matango seem to retain some rudimentary scraps of their host's intelligence. At least enough to identify and distinguish unassimilated victims from other Matango and attack them.
A Matango hive appears as a mini-boss in Godzilla: Monster of Monsters, and can attack using the Mushroom People.