Here is the full list of all 13 Stones of the Revenant achievements worth 1,000 gamerscore.
Defeated the Reaper
Defeated the trickster mage Mordrah
Defeated the Necromancer
Defeat the Banshee of Nalde
Defeat the pharaoh Akhen
Defeat the Revenant
Complete the game solo as Radcliffe the Knight
Complete the game solo as Fritz the Tinkerer
Complete the game solo as Galina the Ranger
Complete the game solo as Isaak the Thief
Complete the game solo as Brielle the Sorceress
Complete the game solo as Halvar the Barbarian
Complete the game co-op