Sarasaland Adventure v4.0 (SMBX) - Lethal Laboratory (7-6; both exits)
Info: https://rpgmaker.net/games/4216/
This level is similar to level 5-3 in which you have to locate keys to unlock the doors to progress and reach the colored switchblocks, which will allow you access to the lower floor. The lower floor is a large maze in which you must find one of the stars and the pipe that will allow you to reach the end of the level. Overall, this level is pretty difficult, and you will need to be careful in certain areas.
Yellow Switch Route: This area isn't too bad. Just remember that you can't stomp the black goombas; you must take them out with a spin jump or by a Yoshi or something. You need to have a shell to break the key down from the blocks at the end of the path; if you kill the koopa paratroopas on the way by accident, you can return to the pipe that spawns a shell; you'll just have to carry it all the way to where the key is.
Green Switch Route: This is definetly the hardest area in the level. Time your jumps so that you don't end up getting hit by the flamethrowers as they shoot up or worse, end up in the hot tar and dying. Before getting the key, you'll want to use the Billy Gun to bust through the bricks to the far right and clear a path for yourself (you can also use Raccoon/Tanooki Mario's tail), then go back for the key and get it to the door.
Lower Floor Maze: Locate the three koopa troopas and climb the chain to get to the blue ! switch and you're pretty much out of the maze, but don't forget about the star that lies to the left. To reach the secret exit, you have to traverse this area twice; once to hit the blue ! switch, and a second time to get to the far right side to reach that door in the top right corner of the room. This is also the very last level that has a secret exit; this one unlocks the last Special Zone Warp in the game.