The Mushroom Zombie is an extremely rare and quite bizarre hostile mob that was added in the 1.8.1 version update. It shares the same model as the typical generic zombie, but has a mushroom-like texture, like the Moshroom.
This mob has the same behavior as the exact same behavior as other zombies but has no sounds, making it an effective and silent attacker. It is also indifferent to sunlight.
The Mushroom zombie can also be found in the following variants: Baby Mushroom Zombies, Baby Villager Mushroom Zombies and Villager Mushroom zombies and Giant Mushroom Zombies. They can also spawn with armor of any kind and weapons and can catch items.
The Mushroom Zombies spawn only in the Mushroom Island biomes, at any time, making it as common in the day as in the night, unlike most mobs and represent less than 1% of the Zombie spawns.
5% of the Mushroom zombie spawns result in a Baby variant of the Mushroom Zombie, other 5% are Villager Mushroom Zombies (with an unknown value of those 10% resulting in Baby Villager Mushroom Zombies) and 1% is Giant Mushroom Zombies.
Mushroom Zombies can also infect Villagers, like other zombie breeds.
Baby Mushroom Zombies
Baby Mushroom Zombies are a challenging and dangerous foe. They are much faster than regular zombies (as fast as normal Baby Zombies) and are unable to produce a noise, which may result in a quick and hard to avoid death of a player.
They use the same model and size as a Baby Zombie and the texture of the Moshroom.
Giant Mushroom Zombies
This incredibly rare breed of Zombie (the rarest of all) has very unique characteristics. It is a mushroom version of the Giant, being as tall as it and having the same model and behavior, its texture being, however the same as other mushroom zombie breeds.
This very hard to defeat creature has a tremendous 12 blocks tall (6 times as much as other zombies) and only takes damage in its upper part of the body (all hits of any kind of weapon are useless below the belt). It can jump 4 blocks high (4 times as much as the jump height of the Giant).
Unlike other Mushroom variants, the Giant Mushroom Zombie only spawns at night (still in the Mushroom Island biome, however). However, it is also indifferent to sunlight but can't infect villagers.