To unlock the Blasphemer trophy in Assassin's Creed Odyssey, you must first purchase the first episode of The fate of Atlantis (or own the Season Pass) and download Episode 1.
There are a total of 18 Marble Maiden Tributes in Elysium that you will need to destroy. You will need to visit the Question Mark (?) symbols on the map to reveal their locations.
The Marble Maiden Tributes are split as follows:
Pheraia's Retreat (East): 6
Deukalion's Heritage (South): 3
Minos's Faith (West): 6
Asphodel Fields (North): 3