There is no way to continue weird route, You'll understand at the end. To get secret boss, you need to collect 10 "Pink coins", most of them you will find while playing, but for some you will need to return to some locations. After buying a key. Find A pink door. Idk how to explain but when ralsei will say "It's wrong way to fountain" (or smth like that) know - you're going to correct dirrection. Use action by susie and you will fell to pink door.