In the new Return to Castlevania DLC, you can access the Richter mode, an alternate game mode where the player takes control of Richter instead of The Beheaded.
Richter Mode can be accessed from depth 6 in Dracula's Castle. After freeing Richter from his cage, the player can return in a later game. They will be able to interact with Richter's cage and will begin Richter Mode.
Some of the gameplay mechanics are changed up to be more in the style of classic Castlevania games. Movement abilities unlocked by runes are removed. Instead the player starts out with a jump, double jump that moves the player slightly backwards and a roll. In the biome itself the player can unlock two more movement abilities, a dash and an upwards double jump.
For more information regarding the Richter mode, please check these articles from the official Dead Cells wiki: