Grox The Great's Horned Cowl

Developer clothing only comes out of Treasure Bags, which means an Expert or Master world and a Hardmode boss on the floor. Every Hardmode bag can roll this one except Queen Slime's. The odds per bag are low, so the set turns up as a byproduct of boss farming rather than something you can go and fetch in an afternoon.

When it does hit, the clothes come with Grox The Great's Wings, and the wings are the part that changes how you play. The rest is a costume.

The cowl, chestplate and greaves go in the social slots and alter nothing but your outline. Because a full developer set only shows up deep into Hardmode, most people end up wearing it over the endgame armor they finished the game in rather than building a look around it.

Grox The Great is one of the programmers on the game. The set nods at his own mod, GRealm, which has a near identical armor called Grovite.