Coelacanth was available during the Raid Vol. 1 for a limited time. Like all other raid dragons, it is encountered through exploring (except Utahkhan's night time) and after defeating it you can get the Coelacanth Scroll and the Crystal of Coelacanth. The scroll requires 55 of these crystals as part of the 3 main ingredients to create its egg.
Brilliant mysterious egg (currently the only way to get it)
Coelacanth and Purple Lips are somewhat similar in a way. Both are being targeted by people due to the dragons' valuable body part, and they hide in particular areas. In Coelacanth's case, the valuable part that the people are targeting is its golden horns. However, unlike Purple Lips, it can also be aggressive.