From Dragon Mania Legends Wiki
The seventh classified type is Ancient and it is the highest tier of classification in terms of rarity. It mostly applies to Dragons, but there are other instances where gameplay elements have a designed rarity.
In terms of Dragons, this type includes all Dragons that have the Ancient Element as their base Element. Dragons with this base Element have two additional Elements which can be unlocked (awoken); the first upon reaching Level 20 and the second at Level 30. The second Element must be awoken before the third Element can be. Additionally, Trainers themselves must be Level 20 in order to be able to awaken the first Element and Level 30 in order to awaken the second Element. Awakening Elements can only be done from the inside of that Dragon's Habitat.
The first Element will cost 750,000 Gold and takes 1 day to unlock while the second Element will cost 99 Gems and takes 2 days to unlock. While an Element is being awoken, Dragons will still produce Gold in their Habitat but are not available to be interacted with or perform any action whatsoever. Once awakening an Element is finished, the icon will be shown atop their Habitat. These Dragons can only be housed in a Ancient Habitat, regardless of their awoken Elements. Even if an Ancient Dragon does not have any of their secondary Elements awoken, Enchantment Materials matching those Elements will still need to be used in order to enchant that Dragon. Additionally, whenever specific Elements are needed to access some gameplay elements in the game or various battle settings (such as those in Castle Events), Ancient Dragons possessing that specific Element must have it awoken before being allowed access.
A complete comparison of Ancient Dragons can be found here.