The The Serpent's Heart Add-on for Shadow of the Tomb Raider: Definitive Edition has 5 achievements.
Complete the Two Graves Side Mission
Complete the Slayer's Gauntlet Challenge Tomb
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