At Level 51 and Level 90, Dragons require training to become a Titan. But first you need to build Valka's Sanctuary. The success of the training depends on the Titan Wheel. For a successful training, the complete pointer with its base needs to land in the yellow area. If it's a miss, you are rewarded with resources and the odds for your next try improve by enlarging the yellow area. If the Titan Training was successful then your Dragon becomes a Titan, which means he has a new look and better skills.