RyguyRyguy, not sure if you are asking for the true algorithm. But I will let you know I wanted a Pre-Release foiled Atarka, so I bought 4 boxs of it, and 3 were Crater Elmentals and 1 was Volcanic something? So Dragonlord Mythics for the box's tend to be more rare than I thought. Seemed like at Pre-Release everyone was opening one..
ZandartheLegendHe is referring to what is the rate of mythics he can get on pre release boxes from the normal boosters (he referred to drafts). It is actually random. From one box you can open 5 mythics, while at the same time, you may not open any. In a booster box you will almost always get 4 mythics and 1 foil rare (sometimes 1 extra foil mythic, depending on the set).
So it is a gamble, but it is usually a good one, because you are getting 5 random promos with each kit plus the new dice, which are awesome and all 5 of these dice together are going for 12 bucks on ebay.