Dr. Man Fly Mask

Dr. Man Fly only spawns during a Solar Eclipse, and only once Plantera has gone down, so any eclipse earlier in hardmode will never produce this outfit. Eclipses roll on their own at dawn, or you can start one with a Solar Tablet when you would rather not wait. The enemy is common enough in the post-Plantera version of the event that a couple of full days usually finishes the set.

This is a two piece outfit, the mask and the lab coat, with no legwear of its own, so you will be pairing it with pants from somewhere else. Both are cosmetic and belong in the social slots. The mask carries the whole joke on its own, and it works over ordinary clothes if you do not want the coat.