Here is the full list of all 20 Urtuk: The Desolation achievements.
Reach the Underground
Kill Andur
Defeat all leaders of the Shattered
Reach the Swamps
Win your first battle
Start Urtuk at least once!
Win the game
Kill 250 enemies
Reach the Ruins
Win the game on Exploration difficulty
Win the game on Adventure difficulty
Win the game on Veteran difficulty
Win the game on Epic difficulty
Win the game on Desolation difficulty
Kill Ivadd
Kill Amos
Kill Victor
Kill Mandoralen
Kill Turgul
Achieve the Champion trait