Plumber's Hat

Two separate chores. The shirt and the pants sit in the Clothier's stock, but only on a full moon, so you either catch the right night or wait out the moon cycle. The hat is not sold anywhere. It drops from Fire Imps, rarely enough that most people end up with one by accident while doing something else in the Underworld.

If you do want it deliberately, the practical setup is a cleared platform down among the lava so imps make up most of what spawns near you, then a long stay. It is a grind, and the payoff is a costume.

Nothing in the set changes a single number, so it belongs in the social slots over whatever armor you are actually using. It only works complete. The hat on its own reads as a plain red cap and the overalls without it read as nothing in particular.

Blue overalls, red shirt, red cap. It is Mario, down to the silhouette.