Deleted 2 years ago
Just use keys you get as reward from Colosseum (as last option) - in case you are not lucky enough to get atleast one Epic, Mythic or Legendary chest from Colosseum Fight (they do count as Tower chest - BUT it was buggy for me in one event and I has bad experience with this) OR from Tower chests.
For new players or players at low levels - Save gems and use it specifically for Epic chest and in case you are not good enough to get key item from Colosseum event (I think you need 168 for Epic chest - so basically 3 or 4 level up which is easier at low level than at high player level) - also this is usually the first real block for your progress in event goals. (Do not waste your gems for gold/rare chests)