The chance is 1 in 100 in getting an Epic Companion, this gets recalculated every time you buy a pack. That means your chances never get better than that no matter how many packs you buy. My Witchdoctor has 2 Epic Companions so far, but I bought the packs to get gold to level my other Companions. I spent a good 60k in crowns to to get there. At level 37 my lowest Companion is level 34, 21 Companions all total.