The The Forge Add-on for Shadow of the Tomb Raider has 5 achievements worth 95 gamerscore.
Complete the Echoes of the Past Side Mission and discover Abby’s ancient origins
Complete the Forge of Destiny Challenge Tomb
Obtain a Bronze, Silver, or Gold medal in Time Attack for the Forge of Destiny Challenge Tomb
Obtain a Bronze, Silver, or Gold medal in Score Attack for the Forge of Destiny Challenge Tomb
Obtain the Grenadier Skill, equip the Umbrage 3-80 Shade weapon, and Brocken Shadow outfit