Bluetracker
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PSA: Rebucketing has occurred. No official confirmation on changes to class balance (microadjustments)
Rebucketing has occurred sometime before 14:00 PDT on August 15
Some players have observed that certain cards are being offered along with cards not previously offered together in the past week since Saviors of Uldum launched.
Notable neutral cards such as Fungalmancer and Wrapped Golem are now seen with cards that were previously known to be in the top bucket or bucket 1 when they were previously offered along middle bucket cards.
There has been no official statement regarding the rebucketing of cards as well as no mention of any updates to class balance (microadjustments). I am keeping an eye on the official forums on multiple language/region sites as Community Managers have typically posted about these changes in the past.
Note that microadjustements refer to specific parameters that every single card is individually assigned and is separate from other modifiers such as set, class, minion/spell/weapon, and rarity.
Keep in mind that Blizzard did not publish or share any bucket information at the start of the expansion and Arena Rotation. Official bucket information from prior rotations has been used to get a general idea on how both Uldum cards and cards from LoE were bucketed; however cards from previously bucketed sets may have been rebucketed for the current Arena Rotation at the start of the Rotation last week.
Iksar
Microadjustment balance changes are based on a formula that takes into account the current bucket information, which is why they don't happen until at least a few days after bucket adjustments. I believe we sent over the public bucket information a few days ago to our community team but it's possible it didn't get to the right folks. I'll doublecheck Monday.
For 15.4, we're going to try doing an arena patch without buckets and have all cards be part of one giant pool. This is similar to how the early days of arena worked. Theoretically, buckets made individual arena decisions a little more interesting and put more weight behind how a card works in the deck you are drafting vs its power level in a vacuum. While I think there is some truth to this, I don't think it's been a well received change overall. For players new or inexperienced with Hearthstone, the idea of having 'obvious' choices is a win. For hardcore players, if the change to buckets is not a clear upside (which has been most of the feedback we've received here) then it's probably just not worth doing. One positive part of not doing buckets is that the micro-adjustment patches should happen faster in the future because there does not need to be a preliminary bucket adjustment patch to set the stage.
Iksar
Glad to hear it :).