Star Princess Crown

The crown and dress only come from the Traveling Merchant, whose inventory rerolls on every visit, so there is nothing here to farm. You check him when he arrives and you either see it or you do not.

There is one useful tell. The set is always stocked next to the Celestial Wand, so if the wand is on his list the outfit is too. Buying both at once is a heavy hit for a purely cosmetic pickup, and he leaves at dusk, so keep a reserve of coins set aside if you collect vanity.

Both pieces go in the social slots and do nothing mechanically. The design points straight at Rosalina from Super Mario Galaxy, and the wand sold with it fills in the Lumas, which is why the two never show up apart.