The Admiral's Success: a Guide on Sailing the Styx

From publisher blurb: THE ADMIRAL'S SUCCESS is a companion and guide for Dungeon Masters leading gaming groups into the treacherous waters of the River Styx. Hours of adventures, be it in the fiery hellscape of Avernus, the cold expanses of Calia or the maddening infinite layers of the Abyss. The Great River hides ancient secrets and horrendous monsters that will amaze and thrill all adventure parties that sail it. Venture down the lower planes and explore 10 new encounters tailored for the true Stygian experience as well as new creatures, expansive lore, new machanics and an unique magic item!