The idea is to eventually use the data to make micro-changes to every card in every class. When and if that were to happen, I would expect it to make a large impact on class balance and to be explained in detail with the community. Essentially, making changes to only a few cards at a time started to feel like it wasn't going to be sustainable. If Fiery War Axe showed up at 5X the rate it did now it would be good for class balance percentages, but less good for actual gameplay. Something else that doesn't feel sustainable is just making better standalone cards for weak arena classes, and vice-versa for strong arena classes. In the next set we could make all Warrior cards high power level and not need a particular style of deck to be strong, but that would probably have a bigger negative effect on constructed that it would have a positive effect on arena. So as of now, we're doing some experimentation with what would happen if we made extremely small changes to a wider variety of cards. As we learn more about it, we'll explain in more detail what a plan of action might look like.

There are a lot of small tweaks going on in the background with the hope we can gather enough data to be confident enough to make a larger scale change. When we do announce arena changes it's generally when we want to set the expectation that arena is going to feel different next time you enter. In order to execute on a long-term solution for arena balance, we've been making very small changes that have an extremely low chance to be noticeable from a single player's perspective, but gather enough data for us to see the overall effect on a classes win rate if you make X card (or cards) show up X% less or X% more. We are talking 1-5% in most cases. Truthfully, the 2X to 1.5X Un'Goro rates were something we should have put in patch notes. I elected to hold back on the micro-changes we were making to gather data in order to not set expectations that things would feel different, but also grouped the set bonus changes into that decision. If and when we make changes to how much the most recent set shows up we'll make sure that is communicated going forward.

This does happen to some extent, and has traditionally happened in most sets in the history of Hearthstone. When Un'Goro released, that set was twice as likely as any other individual set to appear. When 8.2 released, we reduced the rate at which Un'Goro appeared to 1.5X as likely. The idea is that when the a set releases, arena should feel fairly new and different with the injection of new cards at a greatly increased rate. As time goes by and people get used to the arena meta, we reduce that rate.