Board Thread:General Discussion/@comment-4519633-20141022032431/@comment-25926288-20160529111540

ΚΟΜΙΞ wrote: We don't know who of the gods or which supreme being gave the HG. It could be the strongest god of all. Also, DO Dagger/Excalibur has the power to kill all kinds of immortals. Hades didn't try to comfront Rumple with the Dagger... Only through a Deal.

Both the Olymbian Crystal and Excalibur/Dagger can kill immortals but they function in other ways. But Hades ignored the dagger. It's likely that the dagger can't kill Olympians as Rumple and the ever suggested and the book only ever said the crystal could.