Level 1 - Bone Dragon
Level 2 - Golden Dragon
Level 3 - Black Dragon
Level 4 - Magic Dragon
Level 5 - Crystal Dragon
Level 6 - Rusty Dragon
Level 7 - Azure Dragon
The idea is, of course, absurd, especially considering that the first 3 are already occupied by different castles, and they are all level 7 (but this can still be fixed - their characteristics can be changed).