Board Thread:General Discussion/@comment-26580042-20160826010854/@comment-25926288-20160826011408

Well, I spend way too much time analyzing Once's...ahem "magic system". I call it HG magic.

When Emma tethered Hook to Excalibur, she turned him into a Dark One by taking and corrupting Merlin's HG magic. The Dark One is simply a person cursed with the blessing of HG magic. aka they broke the rules and are paying the price.

Merlin's magic became Hook's and now it all belongs to Rumple.