Seasons on Epics follow the calendar year (2017, 2018, 2019, etc). Every year Epics will release a new core collection and then several more limited edition cards and add-on collections for the new season. 

The core collection is the base set that every collector must fill out in order to 'complete' that season's collection and receive any achievements for the season. You can learn more about the cards in the core collection here The core collection for each season currently contains the following card types:

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