From publisher blurb:
The Foresworn is an imposing figure of dread and defiance—a warlock who dared to sever the pact with their otherworldly patron, attaining a cursed form of immortality as a result. Their skeletal visage is wreathed in perpetual flames that neither consume nor comfort, serving as both weapon and symbol of their eternal punishment. Clad in tattered robes bearing the faded insignias of their former allegiance, the Foresworn roams the planes, forever hunted by the vengeful forces of the patron they betrayed. Despite their decayed form, they wield formidable eldritch powers, their mastery over dark magic undiminished and perhaps even amplified by their cursed state. To encounter a Foresworn is to face the wrath of a being who has defied gods and demons alike, wielding the fires of damnation with a will unbroken by eternal pursuit.
Like the Lich is an Undead Wizard, this is an exploration of other 5e Classes into undeath and eternal life, including background and stats.