So, you should have finished stage 3, which means you are supposed to go back to stage 2 (sewers) and make an lightning block at the top, where the 3 fire platforms are. Also yes, you need fire.Hello, i'm really sorry, but i'm too dumb to understand where to go after the second fight with the ghost girl on the fountain.
i have the light paint.
Also no worries, this game can be a bit confusing at times.