Graveyard

The count is taken from a large rectangle centered on you rather than on any fixed point, so the biome travels with you and can form anywhere, including underground. Five Tombstones inside it start the visual side: color drains away, lightning flickers in the background, mist gathers along the floor. Seven complete the biome and switch on the mechanical effects, and past nine more stones change nothing. Each Sunflower inside the same rectangle cancels one stone, which is the lever you use to control the whole thing.

Its own enemies appear in daylight, and so do the ordinary night creatures, which makes this one of the few places you fight nocturnal enemies at noon. Nocturnal bosses still need real night. The spawn rate itself is not raised, but the suppression that normally keeps a town quiet is weakened, which is why a graveyard forming around your base is a problem rather than a novelty. Fighter enemies also pick up a small chance to open doors and tall gates without a Blood Moon, so a closed door stops being a wall.

The mist on the ground acts as a crafting requirement for a set of recipes, so a small graveyard beside your crafting area earns its space. Shop stock changes inside one as well: the Dryad will sell you the seeds of whichever evil biome your world did not generate once you reach Hardmode, which is the cheapest route to having both in a single world, and the Mechanic adds Spectre Goggles. Early on, a flat cleared graveyard is also the standard way to farm Abigail's Flower, which is a strong summon weapon to be holding that soon.

Stones pile up wherever you keep dying, which means your arena and your spawn point. Ghosts in particular hit far harder than anything else you meet at that stage. On Mediumcore this turns into a trap, since every failed attempt to recover your things adds another stone and strengthens the biome further. Ring the area with sunflowers so the count never reaches the threshold, or leave single tile gaps in the floor and platforms so dropped stones have nowhere to land. A Peace Candle takes some of the edge off one that already exists.

Town NPCs complain about living in a graveyard but their happiness is untouched, because it is always layered over a real biome and that biome is what they price against. The Painter is the exception worth knowing, since he refuses to sell his daytime paintings while standing in one. Underground, a graveyard produces mist and no enemies. The mist also coats surfaces thickly enough to hide pressure plates, which is a real hazard if you built traps there before the stones arrived.