The net result is that all of the cash shop methods of acquiring the current crop of dragons will be retired on April 20th, which is (not coincidentally) when the new round of dragons will be introduced. You will still be able to pick up the old dragons in the Dragon Scale or Dragon Token shop, but that will be the only way. So it’s out with the old, in with the new, and if you really want those existing dragons, you should work on that before next Thursday.
TERA first introduced its current crop of riding dragons? Maybe. But now those dragons are boring and dumb, and so your interest can only be retained by the introduction of new dragons that are much cooler than the old, boring dragons. That’s why the game is bringing out a new crop of bone dragons and telling all of the old versions of dragons to take a hike and never come back.
Source: Official Site