Common - Rare - Big Rare - Epic - Legendary - Mythic
For the pussy market event, my current mission is "open epic chest in tower 1 times". I have came across 2 legendary and 1 mythic chest for more than 100 fights in tower but not even a single epic chest.
Suggest more rare chest could replace the less rare one so that we will not be stuck by this kind of mission.
I like the suggestion to allow a more rare chest to be used for event goals. The chests do seem to have different drop rates, with mythic chests the least often for me.
I should mention that later event goals do include open a legendary chest 1 time, and the last event goal is open a mythic chest 1 time.