Polymorph Achievement in Assassin's Creed Origins
Complete tours with at least 5 different characters
How to unlock Polymorph
From the pause menu in Discovery mode, you can go to the Characters tab and change which character you're playing as at any time. Simply complete a tour as 5 different characters to unlock this achievement. Since you have to do 20 tours for "Archeologist" anyway, make sure to change characters between tours to unlock this achievement along the way.