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the most efficient way to get mythic bees is to buy around 25-30k jellies for each from the royal jelly shop. if you can't consistently afford that, i'd recommend upgrading your equipment, buying hive slots if you feel necessary and finishing every questline. black, brown and dapper bears can give mythic eggs from their quests.
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If you really need mythics I would recommend grinding for royal jelly, then setting it to gifted legendary auto jelly. This way you can get gifted legends, they are not as rare as mythics and auto jelly even sorts mythics out and lands on them.
Royal Jelly,Buy them
Mythic:Gamble with them with the Royal Jelly you got
What do you think?