Christmas Tree

Four slots, one each for a topper, a garland, bulbs and lights, and swapping any of them for another of the same kind works at any time. Clearing a slot back to empty does not. The only way to strip a decoration off is to break the whole tree with a pickaxe, which drops everything it was wearing back to you, so nothing is lost beyond the minute it takes to set it up again.

Santa only trades during the Christmas window and most of the decorations come from him, so a tree you plan to leave standing all year is worth finishing while he is still in town. There are more combinations than anyone will ever place, and the toppers are the only part visible from a distance.