Steampunker

She wants two things: an empty house that meets the usual requirements, and one dead mechanical boss. Any of the three counts, so she usually turns up right after your first real hardmode kill, which is good timing because most of what she sells is aimed at the mess hardmode just made of your world. Strictly speaking the world does not have to be in hardmode at all, only a mechanical boss has to have died, and a couple of the special world seeds hand her to you at the start. In one of those pre-hardmode setups she withholds the hardmode-only lines until the world crosses over. She is also armed, and will shoot at anything hostile that wanders near her house.

She is the reason the world stops rotting. The Clentaminator is one of the most expensive purchases in the game and it is worth every coin the first time you watch it eat a corruption tunnel in a few passes instead of an afternoon of mining. Treat it as a savings goal from the moment she arrives. The ammunition, not the tool, is the real planning problem.

The cleanup color is the one she keeps stocked almost everywhere, and it is what you spray to strip corruption, crimson or hallow back to plain ground. The one that plants hallow only appears while she is inside hallowed territory, so you need a patch of it before you can spread more of it. The two evil colors are the awkward ones: each is tied to the evil your world was generated with, and she only offers it while a blood moon or a solar eclipse is running. If you are deliberately seeding an evil biome to farm its materials, that is a night job you have to plan around the calendar.

Buy in bulk before you start spraying. Running dry halfway down a chasm and walking home is the standard way a cleanup session dies. After the final boss she adds three purely decorative colors for painting grass and sand, which are worth a stack each if you build. She has no version for the mushroom biome: the Truffle sells that one instead.

A large part of her stock is crafting stations, and each one only appears while she is living in the matching biome. Rather than building her six houses, move her once and buy the whole list, then move her again: a Queen Statue or a short teleporter chain does this in an afternoon. The graveyard station is the easy one, since a handful of gravestones creates the biome anywhere you like. The Sky Mill is the awkward one, because it wants her up in space, where a platform shack is simpler than a real house. The jungle keeps a second station in reserve for after the temple boss is dead.

The Steampunk Boiler has its own gate: the three early bosses all have to be beaten in that world. In an old world where you never fought one of them, or where trophies came from elsewhere, you may have to go back and kill them again before it shows up.

Her flight gear and her clothing rotate on the lunar cycle, and each occupies the half the other does not. The Jetpack appears while the moon is filling out, the steampunk outfit while it is emptying, so if you check her once and decide she does not stock something, check again a few nights later. Steampunk Wings ignore the moon and wait on the temple boss instead. The goggles only exist around Halloween.

The Blend-O-Matic is cheap and easy to overlook, and it produces asphalt, which is still the fastest floor you can lay in a boss arena. The Static Hook is the grapple most players settle on for the rest of the run, because you control the reel yourself instead of being yanked to the anchor. She also owns the wiring shelf: gates, indicator lamps and conveyor belts all come from her, so a serious contraption needs both her and the Mechanic. If she is parked in a biome with a pylon slot and has a neighbor, she sells that too, which is often the cheapest way to finish a teleport network.

If she happens to be named Whitney and you kill her, she drops a plant named after one of the developers. Dunking her in shimmer swaps her appearance for an alternate look and changes nothing else. In the ending credits she is shown building the Cyborg, though her dialogue suggests she has no idea who he is.