During the eighteenth Devil May Cry DMC Mission: Demon’s Den, you can collect one secret key: Argent Key. DMC Argent Key can be found in the first tunnel, on the right side from Virgil. Jumping in the first gap will leads you to the Argent Key certainly.
Secret Key 1 – Argent KeyLocation: Mission 18 – Demon’s Den
Required ability/weapon: None
Additional Information: This Argent Key is pretty easy to find. In the first tunnel on the right side from Virgil, jump in the first gap and you will find the secret key at the end of the tunnel.