Second to Last level Right?
Maybe Underwater Lava Pits and Fireballs?
Perhaps make it like a sunken part of the The final castle, could be cool to have a 2 part final level.
Actually, I made 1-1, 1-2, 1-3, 1-4, 2-1, 2-2.
I'm trying to make 2-3 and 2-4.
And that'S the whole stage.
Also, your idea is great!