Well yesterday I obtained my BBD and everything was looking down, Galaxy and Rainbow in graveyard, low stone and wood and trolls attacking continously. After spending 5 cash on graveyard I accidently put Galaxy Dtagon and Black Bahamut Rider in Soul Mixer. Well thank you for the accident! I accidently mixed two dragons for a strong 3-Head Primal Dragon! Now I'm LVL 25 and know who to mix!
By the way if you don't know 3 Head Primal Dragon's main stats:
Health: 4700 (4900 With Rider) Attack: 114 (139)