Doom has seen its fair share of mods before, including a remake of Castlevania within the GZDoom engine. Originally announced in 2017 and released in the same year, Castlevania: Simon’s Destiny has only now finally been finished, and recreates the entire NES classic within the first-person perspective of Doom.
Modder Batandy (who also did that cool P.T. remake in GZDoom) states that Simon’s Destiny is a “game born as a love letter to this legendary franchise”, and best of all, it’s completely free! You can grab the mod (which requires GZDoom to play) from Batandy’s itch.io page. Also, make sure to follow the instructions on Batandy’s page to get the game set up correctly.