New achievements are being added in Patch 20.2 which track your overall progression in Hearthstone's rewards track. As you earn progress in each of the different tracks, your overall progress will get updated and allows you to unlock some really awesome-looking hero skins.

The new skins are all drawn with World of Warcraft's Tier 2 armor, so we've got the classic heavy-hitters of Judgement Paladin and Dragonstalker Hunter, which gives us a sweet reward for heavy progress.

Rogue gets the Tier 5 armor set, Deathmantle, not Tier 2 since Valeera already uses Bloodfang armor.
Demon Hunters don't have a Tier 2 set so they have something different as well.

Not a whole lot was mentioned in the original patch notes though, just that we'd be seeing the addition of these portraits to the game. Celestalon later confirmed on Twitter how we're going to be getting them:

  • Every 200 levels you get on the rewards track, overall, not in a single track, gets you a Tier 2 hero skin.
  • These are retroactive so your leveling in the Darkmoon Faire pass counts.

So it looks like these are going to be quite rare to start considering the original base track gave us half as many levels as the new one. Do these new skins incentivize you to want to grind more Hearthstone?

Quote From Blizzard

We’ve also added a new progression achievement, Tavern Regular, which tracks total reward track levels earned on your account across all reward tracks from each expansion. Completing each tier of this achievement will reward a choice from 1 of 10 new Hero skins, featuring upgraded armor!

Quote From Chadd Nervigg

These are quite difficult to get, definitely prestige items. Every 200 total levels on reward tracks gets you a a choice from that pool of hero skins. (Accumulates across reward tracks, and does count retroactive progress on Darkmoon and Barrens reward tracks.)