Blizzard has announced the next patch for Hearthstone. Called version 18.4 by our friends, the update will launch the limited-time "Masquerade Ball" event, bring back the "Dual-Class Arena," and a new "Hearthstone Book of Heroes" featuring Rexxar The new Hearthstone Book of Heroes featuring Rexxar will be implemented. Elementals have also been added as a new minion type in Battlegrounds, while everyone's Battlegrounds ranks have been reset (more on that later). Phew. Let's get down to business.

Nerfed this time around are Guardian Animal and Tortoran Pilgrim. The latter was essential to Turtle Mage, one of the nastiest decks in Hearthstone.

Starting in 18.4, Tortollan Pilgrim's Battlecry no longer finds and plays copies of spells from the deck. This makes it impossible to use Tortollan Pilgrim to draw a copy of Illusion Pill and then use it to copy Tortollan Pilgrim to set up the tedious loop that was the whole of Tortoise Mage. This change should effectively eliminate the deck's win condition, but someone with a better brain than ours might somehow find a way to save it.

Another nerf was to Guardian Animals, a seven mana druid spell that summons two beasts costing five mana or less and gives them a rush, combined with Lake Thresher, Twilight Runner, and Teacher's Pet. It was particularly obnoxious when used. Thanks to the abundance of ramp cards like Druid's Wild Growth, Suppression, Bush, and Breath of Dreams, getting to seven mana was a piece of cake.

Blizzard probably chose the simpler option of either changing multiple ramp cards or hitting Guardian Animal. It remains to be seen if a change of one mana will put the deck at a disadvantage, but small cost changes can often have a big impact.

Guardian Animals and Tortollan Pilgrim will be eligible for a full refund of dust for two weeks after the patch is released.

As for the Battlegrounds rating reset, Tian, a data scientist on the Hearthstone team, detailed the update and the reasoning behind it in the Developer Insights blog. The main change is that all players will receive two ratings: a visible external rating and an invisible internal rating.

The invisible internal rating exists only for matchmaking and is based purely on match results; as Tian explains, "The overall distribution of internal ratings should follow a bell-shaped curve. We may enforce this distribution by performing a procedure sometimes called 're-normalization' on your internal ratings"

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Although essential for matching players of the same skill set, the internal rating will be disappointing. Because internal ratings are rated on a curve, the average player will not be able to keep up with the game and will remain in the middle of the pack, even if they steadily improve at the same pace as other players. To encourage improvement, there must be a way to compare today's skill with yesterday's, and that is what the external rating system is for.

"The main purpose of the ratings is to provide seasonal 'progress' and to partially or fully reflect actual skills," writes Tian. The external ratings are displayed in the lobby interface and will be reset to zero for everyone in this week's 18.4 update and again at the start of each subsequent season, but the ratings will be adjusted quickly to compensate for any discrepancies. If the internal rating is higher, the external rating will tick up faster, with the gains multiplied by the modifier. This modifier is proportional to the discrepancy between the internal and external ratings." This can be thought of as a process where the external rating 'tracks' the internal rating. If the external rating exceeds the internal rating, the chase will stop."

The maximum external rating increase per match is capped at 300 points, and players scoring below 6,500 points are given "a very small positive rating increase" per match as an incentive, regardless of the outcome.

Meanwhile, a protection zone is established at the start of each season to prevent external ratings from falling below zero. In addition, a "floor" is established every 500 points between 2,000 and 6,000 points to prevent a few bad games from going below that. At the very least, knowing that a tangible number remains a permanent indicator of past success will ease some of the disappointment of a loss.

Psychologically speaking, comparing yourself to your past is always healthy and a better motivator to improve your actual skills. However, when it comes to fictional heroes, you should definitely compare. Here is a tier list of which battleground heroes to choose and which to avoid. Don't let Professor Putricide see this.

The dual class Arena and Elemental will go live on September 29, and Rexxar on October 13. More information can be found at playhearthstone.com.