The Shofar or Ram's Horn was the only weapon known to harm Osiris. Sam and Dean needed the horn to take down Osiris after he sentenced Dean to death. Dean stayed in a ring of salt, to protect himself from Jo's ghost, while Sam went to steal the horn from a synagogue. Sam found the horn but was caught by the synagogue's rabbi. It is unknown as to how Sam managed to convince the man, but Sam stabbed Osiris just before Dean was about to be killed.