What is flames of phlegethos?

Flames of Phlegethos is a magical item in the popular tabletop role-playing game, Dungeons & Dragons. It's a rare wondrous item that resembles a pair of red-hot brassieres. When worn by a character, it enhances their fire-based spells and attacks, making them more powerful and difficult to resist. It also has a secondary feature that allows the wearer to create a magical wall of flames that damages enemies who pass through it. The Flames of Phlegethos are named after the infernal plane of Phlegethos, a fiery realm of devils and demons in the Dungeons & Dragons universe.