Just a bag of bones.
Skully is one of the few craftable mounts in the game. Like all other craftable mounts, they can be made at an Adventure’s Crafting Bench with materials, however these materials vary, but Steed Feed in various quantities are always a requirement. For crafting Skully, players need to gather Somber Souls from mining in the Cursed Vale and Bleached Bones from undead enemies (which can be found in oth Cursed Vale, Desert Frontier, and Permafrost Biomes).
Skully is a Reference to the X-Files.