FNF vs Gaster [Gaster FNF mods]
Gaster (W.D. Gaster) is a secretive character from the game Undertale. You can meet him by scoring 66 points in 'FUN' mode in Undertale. From what we know, he was the first Royal Scientist before Alphys, and died of unknown causes related to his experiments.
Gaster in FNF mods
In Friday Night Funkin, Gaster challenges BF to a battle, if he wins, he can get his body back, if he loses the battle, he will disappear. Line-cracks on his head appeared after an unsuccessful experiment.