Exotic Dragons are available only from permanent Collections.
Just like Defender Dragons, an Exotic Dragon is shown in the Collections menu and you need to gather items or spend to get it. With each item you collect that is required for that specific dragon, the cost is reduced by a certain amount until you gather all items and get the dragon for free (But losing those collected items of course).
When you have already gathered all the items for an Exotic Dragon, and after you have clicked the Trade In button, a new OR the same Exotic Dragon shows up in Collections with specific new items that will need to be collected in order to get that one.
As of the current version of the game, what new Exotic Dragon you can get after Trade In is considered a random pick.
When you complete all the collections for all Exotic Dragons once, all Exotic Dragon collections that come after will be for free.
A player may have more than 1 of the same Exotic Dragon.
All known Exotic Dragons currently in the game are listed below: