At present the cryptic dragon drops a head at .3% often for sale at 200m or more
At present the mystic dragon drops a scale at .3% often selling at 150m or more
Here's the odd part to consider adjusting. The mystic dragon may also drop a hoard of gold at .1%.
It is the hardest drop and how much is it worth? Only 10m gold!
![:-O :o](./images/smilies/icon_e_surprised.gif)
I think being the most difficult drop it ought to have a higher value than the others, perhaps 100m instead. I suggest 100m because the heads and scales though worth more you do have to find a buyer for them.