The The Serpent's Heart Add-on for Shadow of the Tomb Raider: Definitive Edition has 5 achievements.
Obtain a Bronze, Silver, or Gold medal in Time Attack for the Slayer's Gauntlet Challenge Tomb
Obtain a Bronze, Silver, or Gold medal in Score Attack for the Slayer's Gauntlet Challenge Tomb
Obtain Divine Bounty skill, equip Serpent Lash Godslayer weapon and Dragon Scales Legend outfit
Complete the Two Graves Side Mission
Complete the Slayer's Gauntlet Challenge Tomb