The Hearts of Stone Add-on for The Witcher 3: Wild Hunt has 12 achievements worth 450 gamerscore.
Kill 20 cows.
Collect all available Ofieri armor and horse gear, and at least one Ofieri sword.
Provoke all Iris von Everec's Nightmares into fighting you at the same time and defeat them.
Recreate all of Iris' nightmares in the Painted World.
Participate in all the activities at the wedding.
Buy all the items put on the block at the Borsodis' Auction House.
Slide downhill uninterrupted for at least 10 seconds.
Defeat all the fallen knights and loot their campsites.
Kill 3 opponents with their own arrows.
Finish the "Hearts of Stone" expansion.
Be under the influence of seven potions or decoctions at the same time.
Kill the prince cursed into a toad.