It can be hard to play the Arena as a new player, particularly because the game mode has a special rule set that's frequently adjusted by Blizzard. Until now the only way to know of such things was to piece it together yourself through various patch notes or comments from game designers on social media. Recently, the developer released all of the relevant balance information in the 8.4 Patch.
Looking for an introduction to the Arena? Check out our new player guide.
Here are the current Arena rules:
Appearance Rate Adjustments
Not every card is equal in the Arena. Over time Blizzard revealed that certain types of cards had a much higher impact so they now appear less. Weapons, on the other hand, were almost too rare for the classes that use them so they've been adjusted to appear more frequently.
Note: Neutral cards form the basis for draft appearance rates.
On average, Arena runs consist of 60% Common, 28% Rare, 10% Epic, and about 2% Legendary cards.
Class minions are +100% more common than neutral cards.
Class Spells and Weapons are +175% more common than neutral cards.
Journey to Un'Goro cards receive an additional +50% increase in their appearance rate.
Popular cards have had small drop rate changes to address class balance concerns. (Note - These changes range from 1-10% in total. They are small enough that they are unlikely to be noticed during an individual draft, but should have enough cumulative impact to help improve class balance.)
Some cards have been removed from the format for balance reasons. Quests aren't likely to ever have enough synergistic support so they've been removed. The same can be said for C'Thun and any of the cards that buff it. Others like Succubus and Purify were previously removed to help with class balance.
Want some more reading on the Arena? Check out our new player guide talking about how to play the Arena, drafting your deck, Arena rewards, and more.