The The Hidden Ones Add-on for Assassin's Creed Origins has 8 achievements.
Complete Main DLC Quest "The Greater Good" (The Hidden Ones)
Assasinate Tacito, Ptahmose and Ampelius (The Hidden Ones)
Free 20 Rebels (The Hidden Ones)
Perform 3 Assassinations from a zipline (The Hidden Ones)
Complete Side DLC Quests "Rise of Shaqilat" and "Shadows of the Scarab" (The Hidden Ones)
Perform a leap of faith from Arsinoe's sundial obelisk between 10 am and noon (The Hidden Ones)
Complete the Walls-of-the-Ruler citadel (The Hidden Ones)
Kill an enemy with a headshot while they are being harassed by Senu (The Hidden Ones)