Board Thread:Spoilers!/@comment-9241531-20160516162716/@comment-1916997-20160516223811

I honestly don't have any theories right now, other than Rumple probably did a deal with Jekyll/Hyde at some point before the first curse, which at the very least explains how they know each other. It is also possible that Rumple banished Jekyll/Hyde from his homeworld (which I'm headcanoning as LWC right now) to the LOUS. I'm sure Season 6 will answer most, if not all, of your questions regarding this though.