Santa Claus

Two things gate him and only one is permanent. You need a spare valid house, and you need the Frost Legion beaten in that world at least once. Once that kill is on the books it never expires, so he returns every year without you repeating anything, which is worth knowing before you tear down the arena. The house has no special requirement beyond being empty and legal. What he will not do is arrive out of season, however good the housing situation is.

He exists only while the Christmas event is running, which the game reads off your system clock across the back half of December. When the window closes he does not pack up and leave, he dies at the next sunrise and you wait a year. There are ways around it. Reaching the fifteenth wave of the Frost Moon buys a single in-game day of the season at any point in the year, which is enough for one shopping trip if your coins are already counted out. Changing the machine's date is the usual approach and works on every platform, with the console versions needing you to drop offline first. The jingle all the way seed leaves the season switched on permanently.

He is normally a hardmode arrival because the Frost Legion is, but the condition is the kill rather than the state of the world. Carry a Snow Globe into a fresh pre-hardmode world, break it, beat the Legion there and he will move in with the full shop while you are still swinging early gear. It buys decoration rather than power, but it is one of the few genuinely useful things a globe can do.

None of it changes a fight. Everything here is furniture and vanity, and the reason to plan the visit is availability, not power: the Christmas Tree and every ornament that hangs on it exist nowhere else, and the store shuts for a real calendar year the moment the season ends. Buy the trimmings in bulk on the first trip. Garlands, bulbs and toppers cost so little that the only real expense is having to come back, while the Santa Hat and the rest of the outfit are the part that actually dents your purse. Nothing in the stock is gated behind anything else, so if he is standing in the house the whole list is open to you.

He carries more items at once than nearly any other vendor, and his final slot is permanently occupied because of it. That slot is the one the game normally uses to hold something you just sold, so with him there is no undo. Sell him the wrong thing and it is gone for good, which is a real risk given how much junk people offload while emptying an inventory into a shop.

He is not helpless when something wanders into town. He throws baubles at nearby enemies, which is quietly useful during the Frost Moon if his house sits anywhere near where you fight, though nobody should be counting on him for it.

He has exactly one possible name, fewer than any other townsperson, and the housing menu labels him Santa Claus the Santa Claus. He is the only NPC who outright loves and hates a biome rather than merely liking or disliking one. His feud with the Tax Collector is a Christmas Carol joke, since that character is built on Scrooge. Shimmer gives him a look borrowed from Ded Moroz, the Slavic version of the same figure.