Little Known Egyptian Myths: Seth Steals Osiris' Corpse (Papyrus Jumilhac)
The story goes that each evening at twilight, Anubis would take a break from embalming the murdered god and leave Osiris' corpse alone for a short time. Seth, watching from a safe distance, observed Anubis' movements, and one evening, seeing his chance, transformed into the jackal-headed god and slipped past the guards, who failed to recognize him. Unchallenged, Seth stole Osiris' body and fled, sailing off down the river, soon after pursued by Anubis and his entourage, who quickly realized what had transpired. When the two gods met, Seth transformed into a bull to intimidate Anubis, but Anubis caught Seth and tied him by the legs, before severing his phallus and testicles. Anubis then carried Osiris back to the wabet, and imprisoned Seth in a place of torture.
In a similar myth, also recorded in Papyrus Jumilhac, Seth again transformed into Anubis and attempted to steal Osiris' corpse. As before, he was swiftly captured, but this time was sentenced to spend eternity as a chair for Osiris. Seth managed to flee, but was caught and cooked by the gods, and Anubis wore his flayed skin (perhaps as retribution for all the times Seth tried to impersonate him?).