You are right! Good maths

I explained that
HERE, I dont doubt you have read me xD
Cool Fire + Cool Fire have way higher than 50%, I say it is around 70% chance to get legendary dragon(not the one you want)
In 10 tries I got 10 legends, thats 100% there, I am going to keep trying until I get mirror, so I can get more calculations from it!
But if you talk about getting the legendary dragon you want, It supposed to be the %/4
so 70/4 = 17,5% chance to get each legendary dragon!
Ofc, I got 5 winds, 3 legends and 2 crystals, no mirror yet, I hope the mirror is about to come, if I have bad luck with % I could fail 20 more attempts to get mirror!
It is possible!