The next limited dragon has arrived. And you need a hidden element to breed a Morphimagus dragon.
Stella + hidden
Stella shares fire, earth, cold and dark. And thanks to the Dragonvale Compendium (and Minyaz who taught me how to use the Dragonarium tab) I discovered that Umbra is a hidden dragon that shares earth, cold and dark.
Morphimagus has a 4% breeding chance, meaning 17 attempts are required for a 50/50 chance to breed one. 16.68 hours average fail time, means 11.81 days for an even money chance.