Green Moss

Moss grows on stone as a fuzz that can be cut like any wild plant, but cutting it with an ordinary tool just destroys it. A Paint Scraper or the Spectre Paint Scraper is what occasionally turns that fuzz into a placeable clump instead, and it does so rarely enough that you should plan on scraping a lot of wall for a modest stack. Mossy stone also takes one more hit to mine than clean stone, a small tax you feel when tunneling through a moss chamber.

Only three of the five ordinary colors exist in any given world, and they are handed out one per horizontal third of the map, so the color you keep finding on the left side is not the one waiting on the right. They appear either as scattered growth on open cave surfaces or inside dedicated chambers walled with the matching mossy wall, which is the easy way to spot one from a distance. Lava Moss plays by its own rules and grows in patches down around the lava layer of the caverns.

The four gas named mosses, krypton, xenon, argon and neon, get their own biome, and a world generates exactly one of the four. These areas are far larger than an ordinary moss chamber, sit in the cavern layer usually above the lava, and never generate near the horizontal middle of the map. Bigger worlds get more of them. Helium Moss is not generated anywhere: throw any other glowing moss into Shimmer and it comes back as helium.

None of this locks you out permanently. Feeding glowing moss into an Extractinator returns ordinary mosses, and a Chlorophyte Extractinator will produce any variant in the game. Short of trading, that is the only practical route to a complete set inside one world.

Placed moss creeps outward on its own across exposed stone blocks and gray brick at any depth, including up on the surface where it has no business being. That gives you a free multiplier. Lay a long bridge of plain stone next to a patch you already have, go do something else, and come back to a wall of the stuff. It is the standard workaround for not having found a paint scraper yet. Moss dies the instant its host block converts to ebonstone, crimstone or pearlstone, so keep a moss farm well clear of anything spreading. Strange Plants will grow on mossy stone, and clumps survive on actuated blocks as long as nobody harvests them.

Glowing moss burns at full brightness as a dropped item and inside an Item Frame or an Item Flask, so it works as a light source that does not look like one. Moss and its matching walls convert back and forth, which makes walling a room in a color cheap once you have a supply growing. The glow colors are only loosely tied to what those gases actually do in a discharge tube. Krypton is green here as a Superman joke rather than a chemistry one, and radon is the only noble gas that never got a moss.