(Best in full screen) A close copy of the normal final boss from Hollow Knight, but you couldn't stop the infection on it. (This next paragraph will only make sense if you know the whole story of Hollow Knight) This character was sort of like the game's Hollow Knight. Still, instead of it being your brother like in the game the final boss is a new vessel created because the original Hollow Knight gets overrun by the infection and is sealed away by the pale king leading to the king's death and causing a new Hollow knight to be needed which is filled in by another vessel that was faster to get to it than the player.
Mario 64 for the music Hollow Knight for the idea