The biggest change in store for arena in Update 7.1 is the switch from wild format to standard. This is being done because arena was getting a little too wild, apparently: “Attempting to create decks that utilize these meaningful synergies in a wide and diluted card pool will become more and more difficult as the wild card pool grows larger.”
But wait, that’s not all! Arena will be tossing in a higher percentage of rare cards, pushing out more spell cards than before, holding back boring neutral classic cards, and including players’ own golden card visuals if any are owned.
The update should be coming before the end of the month, so keep your eyes peeled!
Source: Official forums
