Sarasaland Adventure v4.0 (SMBX) - Desert Castle (4-8)
Info: https://rpgmaker.net/games/4216/
I believe that this is the only castle level where you have to play as Peach the whole way through, and it is most definetly the hardest castle so far in the game. There's forms of instant death present other than lava, including the rising and falling spike ceiling, rising and falling floors which can crush you if you're standing in the wrong spot, moving spike walls and to top it off - those dreaded fast moving SMW spike pillars. This is quite a doozy of a level, and one that punishes mistakes. This level requires you to pay attention to your surroundings and you will need to be quick in certain areas, like the room with the rising and falling spike ceiling and the room with the thwomps, and have careful positioning and timing with your hovering in other areas, like the room with the fast SMW spike pillars. One mistake and you're most certainly finished.
Morton isn't too bad; just shoot him to death. It's not easy because half of your shots will probably get blocked by his wand attack or the podoboos. Also there are supposed to be two bony beetles in the room with him; for some reason, they fell into the lava as soon as I entered, which is good for me, I suppose. World 5 is next, and is where the game definetly gets more difficult.