Glowing Mushroom biome

A glowing mushroom biome is mushroom grass on Mud Blocks, with Glowing Mushrooms and giant mushrooms growing out of it, lit blue by the plants themselves rather than by any light you place.

The underground version generates naturally at world creation, usually deep, as a set of wide layered caverns with mushroom vines hanging from the ceiling. It always includes a stretch of flat ground so the giant mushrooms have room, and sometimes a broad lake. The surface version does not generate at all. Every one you have seen above zero depth was placed by a player, unless the world runs the Toadstool seed.

The biome runs on a count of mushroom related tiles, and the numbers do not line up with the visual cues, which is where people get confused. What counts: mushroom grass, the glowing mushrooms that grew on it by themselves, giant mushrooms underground, and mushroom vines.

One hundred tiles is where the area becomes a glowing mushroom biome mechanically. Spawns change, fishing changes, housing counts it. On the surface the background appears at that same hundred and the sky darkens at a hundred and sixty. In the Underground layer and below, the background holds off until a hundred and sixty one, so a patch can already be a working mushroom biome while it still looks like plain cave. Build one and wait for the background to confirm it took and you will overshoot by half again. Watch the spawns instead. The Funkytown achievement wants two hundred tiles near you, which is more than the biome itself requires.

Plant Mushroom Grass Seeds on mud and let the grass spread, or spray a jungle with a Clentaminator loaded with Dark Blue Solution.

The fast way to lay the mud is a grid with single tile gaps rather than a solid slab. Grass spreads across exposed block faces, so a checkerboard gives it far more surface to travel along, and the empty cells fill with plants that count toward the total anyway. A solid block of mud only grows on its outer skin.

The Truffle needs a house in a surface glowing mushroom biome and will not accept an underground one, which is the whole reason people build these. He sells mushroom themed gear, and after Plantera he stocks the Autohammer, the only route from Chlorophyte to Shroomite Bars. For a ranged character that one NPC gates your best armor set.

Truffle Worms only spawn in underground glowing mushroom biomes, and they are the only way to summon Duke Fishron. They burrow the instant you get near, so bring a bug net and expect to waste a few. The Mushroom Pylon works from either version, needs only two houses with residents who are content in them, and requires neither hardmode nor the Truffle, so an early mushroom patch is a cheap extra pylon well before it is anything else.

The jungle is the easiest site, since the mud is already there and all you supply is seeds, and it hands you a second pylon covering the jungle half of the map. A floating island is better still if you have one. The biome brings its own darkness and that darkness spills over everything nearby, so putting it overhead keeps it clear of your surface routine and out of reach of biome spread at once. Leave margin wherever you build: the mushroom background shows up as much as a screen's width from the tiles producing it, so the visual footprint is larger than the real one.

Natural underground biomes are worth colonizing rather than building from nothing. They sit deep, so a base in one is a staging point on the way down, and their flat floors attract everything that needs level ground, which is why Gold Chests, statues and Life Crystals turn up in them so often.

The enemies in a surface glowing mushroom biome are tuned well above the rest of pre-hardmode, so building one early parks a lethal patch of ground beside your base. The fix is residents. Town NPCs cut spawn rates hard, so two houses inside the biome, one waiting for the Truffle and one occupied now by someone like the Dryad, handles the danger and prepares the site in the same move. Come hardmode, spore-shooting Fungi Bulbs and Giant Fungi Bulbs can still reach through gaps, so seal the housing rather than leaving open doorways.

• Mushroom grass cannot be converted by corruption or crimson, so a strip of it works as a barrier against spread.
• Green Solution turns a mushroom biome back into jungle. Purification Powder will not touch it.
• Underground mushroom biomes never generate inside an ice biome or an Underground Desert.
• NPCs housed in an underground one probably register as a cavern town and start attracting gem critters, which are nearly invisible under the blue light unless you add a brighter source.
• Paint one mud block, drop a seed on it, and the color carries through the whole biome as the grass spreads. Deep paints show without a light source; normal paints need one.
• The glow gets brighter toward the center of an underground biome, which is a rough compass when lost.