The Triboniophorus Tyrannus (/'traɪ,boʊniːoʊ,fɔərʌs/ /taɪ,rænʌs/ treye-boh-nee-oh-foh-russ teye-ran-uss), often referred to as the Brain Slug, is a community-created cosmetic item for the Pyro. Triboniophorus Tyrannus is a paintable green, gelatinous slug with beady gloss black eyes, placed off-center atop the Pyro's gas mask-burnished head.
- The description of this item was written by crushilista for the Hat Describing Contest.
- The hat appears on page 2 of the True Meaning comic, wearing a B.M.O.C..
- Triboniophorus is a genus of green slug native to Australia. "Tyrannus" is Latin for "tyrant/despot". The item name can thus be translated from New Latin as "the tyrant slug".