Mushroom

"Wait, go back a minute. Plant life? NO! Mushrooms aren't actually plants. All plants contain a chemical called chlorophyll which they use to turn sunlight into energy, and which also makes them green, but mushrooms don't have chlorophyll at all. Instead, they get their energy by breaking down decaying organic matter. So what are they then? They're fungi, which is a category all of its own, and also includes yeasts and moulds. Fungi don't get as much attention as plants, because they tend to live in soil or underground where they can't be seen. In fact, they're genetically closer to animals than they are plants. Think about that next time you cook up a mushroom stew."

- Duncan Geere

Mushrooms are fungi that grow and spread in dark areas.

Obtaining
Mushrooms can be instantly mined with anything.

Natural generation
Mushrooms naturally generate in poorly lit areas (light level of 12 or less). If this condition is met, each chunk has $1/8$ chance to generate red mushroom and $1/4$ chance to generate brown mushroom.

Mushroom also generate on surface in swamp, giant tree taiga, mushroom fields biomes and anywhere in the Nether.

Witch huts have a flower pot with a red mushroom inside. Mushrooms also generate inside "mushroom farm" rooms in woodland mansions.

Huge mushrooms
Mining a huge mushroom block drops up to 2 mushrooms of the same color.

Fallen trees
$$ fallen oak, birch, spruce, and jungle have 0-2 mushroom generated on horizontal logs.

Mobs
Shearing a red or brown mooshroom drops 5 mushrooms of the corresponding color and turns it into a normal cow.

Trading
Mushroom can be bought from wandering trader for an emerald.

Usage
Mushrooms can be planted and grown on blocks in light levels below 13 and not directly underneath the sky. If planted on mycelium or podzol, they can stay planted in any light level. Both brown and red mushrooms grow at the same rate regardless of the light level.

Besides being mined directly, mushrooms are dropped as items if:
 * the block below them falls, is moved, or destroyed;
 * a fluid flows over them;
 * it is above light level 12 and a block updates next to it and it is not on podzol or mycelium.

Huge mushrooms
When bone meal is applied to a mushroom, the mushroom has a chance to grow into a huge mushroom of the same color, provided that it is on a proper block (dirt, coarse dirt, grass, podzol or mycelium), has enough space, and that the light level is dark enough.

Spread
Mushrooms will spread randomly onto nearby blocks when in appropriate conditions. They will spread only if there are fewer than 5 mushrooms of the same type in 9×9×3 area.

Light source
Brown mushrooms emit a barely visible light level of 1.

Decoration
Either type of mushroom can be planted in a flower pot.

Composting
Placing a mushroom into a composter has a 65% chance of raising the compost level by 1.

Trivia

 * Mushrooms can generate on the leaves of trees.