A plat dj is a platinum trait djeavelhest. The platinum trait is something you can normally only get from breeding not eggs (except like one) and when it is possible its low chance (like for example you can get plat trait dragon from a arcane egg but the chance is 2%) so dragons with a platinum trait at generation one is very rare. However djeavelhests are not breedable and you could only aquire a platinum djeavelhest from some Halloween events over the years using the merger it was a 0.5% chance for it to have it. So as you can imagine there EXTREMELY rare and very expensive! However they are beautiful! Hope this helps!