Tip: If you make a change to your ROM that you regret, just go to File > Restore > Restore ROM to Previous State in the menu. From there, you can select a restore point and revert your ROM to a previous state.
Good luck: This is good, easy to clear but varied, nicely paced and entertaining!
Mario vs Hammer brothers: This level focuses a lot on walking forward and firing fireballs. It gets unexciting after a while. It could be improved by mixing things up by defeating them with Koopa shells (you could hide the Hammer Bros under unbreakable blocks and force the player to kick down shells), Yoshi, P-switches that make the ground turn into coins under them and so on.
Running mario: Pretty much the same issues as Mario vs Hammer brothers.
Easy one: Not bad for a first level, there's some original brick formations in it.
Where is yoshi: The water sections feel like they go on for way too long since there is so little to do. If you want to do swimming between pipes I think a higher scrolling speed would make it less dull. But I really think there should be more to do, perhaps P-switches to pass brick walls or something.
I think Yoshi is completely wasted in this level. There are literally no passages where I thought I had any use for his abilities. First there is a swimming section, then there is the final stretch where the enemies can be eaten and I´m encouraged to ditch Yoshi and climb the beanstalk instead. I would have preferred some use for Yoshi, like a route with spike floor or eatable enemies.
Easy pipe way: This level needs an emergency exit where the hidden door is. If you enter without the P-switch you get stuck in a dead end. The player will need to reset and that´s annoying.
Piper or not piper: This is a nice little level with an easy puzzle in the start. Pretty good.
Long way home: A good labyrinth, and I really like that you've planned some good alternate routes! Perhaps you could consider using donut blocks instead of blue falling platforms in the start, since donut blocks can reappear if they fall down.