“This Hearthstone Update charges the nether coils as we get ready to pull the big, shiny lever that unleashes Hearthstone’s newest Expansion: The Boomsday Project, on August 7! This is also your chance to participate in cutting-edge research: drop by a special Fireside Gathering for a Pre-release Event where you can open The Boomsday Project packs and play with your new cards before the official release! This update also brings Arena updates, game mechanics updates, and a few card changes, as well as some bug fixes and feature improvements.”
So about that Arena update. It’s important that class cards show up in Hearthstone’s Arena format. They help ensure that every class feels different, after all, and that’s pretty important in this particular format. But there’s also the problem of them showing up a little too frequently at this point, which is why this patch is dropping their appearance rates significantly. Class cards will have a 50% drop to their appearance rate, as will spells and weapons, which results in a net drop from 250% appearance to 125% appearance. (It’s a multiplicative thing.)
This update will also lower the appearance rate for rare and epic cards somewhat, although they’ll still be certain to appear at fixed intervals. The full entry includes absolute listings of all the probabilities for the format as it stands now, so if you enjoy picking through that sort of data for analysis, go to town; it’s right there for you to enjoy. Otherwise, just get used to seeing some cards a bit less frequently.
Update 12.0 is now live on PC with mobile launching later this afternoon. This sets the stage for The #Boomsday Project launching August 7th!
— Hearthstone (@PlayHearthstone) August 2, 2018