5how it drops
The bags Hardmode bosses leave behind are the only source and the roll is rare, with Queen Slime excluded. Expert or Master is required, since Classic worlds never produce those bags. Any Hardmode boss counts, so farm whichever one you can put down fastest rather than chasing a specific fight.
two outfits, one tiara
Cenx has two wardrobes in the pool, this one and Cenx's Dress set, and no single bag ever contains every piece of both, so the full collection takes more kills than other developer sets. The overlap helps: Cenx's Wings and Cenx's Tiara come with either roll, so those are the two you hold spares of. With a complete set on you throw off pink glow particles, but only near a light source, so the outfit looks flat in a dark cave and comes alive by torchlight.
the version that fought back
For a stretch these sat in the files with no way to obtain them, and the code punished anyone who forced one into an inventory: wearing any part dragged your movement to a crawl and stapled on debuffs that never expired. That was stripped out when the set became a real drop, and the tooltips rewritten into the joke about impersonating developers.