I played back when Synchro monsters such as Goyo Guardian were a big deal. So I know what these Level 6 Synchro monsters can do. Indeed, the Coral Dragon is already seeing play in Water-based decks such as Atlanteans and Mermails. But because he doesn't have any specific summoning conditions, he's appeared in the Extra Decks of other archetypes as well, including Blackwings, Phantoms, and Heroes!
Coral Dragon is definitely a Synchro Monster that I would want as part of my collection. If I were to build an Atlantean or Mermail deck, this would be at the top of my list for cards to acquire.