Butcher Mask

The Butcher only walks during a Solar Eclipse, and only in a world where Plantera is already dead. Eclipses roll on their own once you are far enough into Hardmode, but a Solar Tablet lets you start one on demand, which is the sane way to farm a costume.

Each of the three pieces rolls off its own kill, so plan for several eclipses before the mask, the apron and the pants are all in hand. Build wide and flat for it. Butchers close the distance in a straight charge, and the same event is throwing Mothrons and Reapers at you while you try to line them up.

It is appearance only, worn in the social slots above your real gear. The mask and the stained apron read as the thing that dropped them, so this is the closest the game lets you get to walking around as an eclipse monster.