In order to reach the Hellfire Knight DLC in Code Vein, you will need to make your way to the Crypt Spire – Upper Level mistle. From there, head north passing through the areas where you fight the Blade Bearer, Cannoneer and Juzo Mido to reach a long hallway with lights leading down it on both sides. Head down the hallway and take a left or right (don’t go down the stairs heading north) to reach a side set of stairs. Head down those stairs to reach a purple door. Unseal the door and head through another hallway to reach a room. It will contain the Fiery Oblivion map. Head back to Home Base with the map in hand and speak to Davis to unlock the Fiery Oblivion depths.