Brimstone from Friday Night Funkin Lullaby is a fan-made FNF test mod that probably took the creator the most time and effort to complete. This Brimstone FNF mod was requested by @DominikLikesScratch and is now available to play online free at fnf.gosprunki.net.
For the best experience, the creator strongly recommends using Turbwarp: https://turbowarp.org/771855023. All credits for this mod go to the Friday Night Funkin Lullaby Team and Funkypedia. If you encounter any bugs, please report them in the comments section.