Today, I present you: The Four mod for Doom!
This ain't new as this was made a year ago. All it does is replace the pink demons with Four from BFB which was made using Paint 3D. The inspiration for this came from a 90s mod where Barney the Dinosaur replaces the demons. I've only tried this out on GZdoom, so its performance may differ on other ports.
You can download it here:
https://drive.google.com/file/d/1sP_A7X2GO8WRgLVPf2EK52paR3D2ul5A/view