Tip: You can use Lunar Magic's Overworld Layer 3 Editing system to edit or create your own layer 3 images (castle bricks, fish, rocks) and apply unique effects per level via the Layer 3 Bypass in the main editor.
Welcome to Mario's 2 Ways 2 Victory (Mario's Two Ways to Victory, or M2W2V for short.)
This is a hack I started a long time ago to test out vanilla resources, which eventually turned out to be a full project. The hack has gone through various modifications since I started it, mostly because the first levels I made didn't match my current criteria on level design. I could have dropped this project a long time ago, but I wanted to have a complete hack and I didn't feel like starting a new one.
The story is a bit of a sequel to the original SMW. When Mario and Yoshi were leaving Dinosaur Land, their ship was attacked by Bowser and the princess was taken in the process. Now Mario and Yoshi have two ways to reach Bowser's castle: they can go through the regular way beating all the Koopalings one by one, or they can find the hidden stars in a mysterious land called the "Land of Magic" which will take them to Bowser's castle.
It's up to you to choose which way they should go. The former is easier but longer, and the latter is shorter but harder. You can also mix both ways.
Note: If you are going to play the hack in Zsnes, change the "per2exec=100" to "per2exec=150" in zsnes.cfg to avoid slowdowns. Other emulators should be fine.