The 20 Year Celebration Add-on for Rise of the Tomb Raider has 11 achievements worth 250 gamerscore.
Finish the game on Extreme Survivor difficulty
Lara's Nightmare: Defeat the Nightmare
Lara's Nightmare: Defeat 100 enemies
Lara's Nightmare: Destroy a Skull of Rage
Blood Ties: Collect all of the Documents in Croft Manor
Blood Ties: Collect all of the Relics in Croft Manor
Blood Ties: Find truth of Croft Manor
Blood Ties: Open Lord Croft's Safe
Blood Ties: Collect 50% of the Documents in Croft Manor
Blood Ties: Collect 50% of the Relics in Croft Manor
Blood Ties: Acquire the Master Key