runouw.com

This level is... confusing.

Despite it being titled "Mario The Star Rescuer Demo", the first sign says "Please note that : this is only the level 1 of this episode. so please, download the FULL.zip file for all levels of this episode.

There is no FULL.zip file linked to in the level's description or in the level itself, so I have to assume it hasn't been made yet. How ambitious.
If I were you, I wouldn't advertise future levels anywhere but my profile and signature.

Mario then faces two large Goombas and finds a castle structure with two doors - they are both locked, as indicated by a sign.
Then he jumps over three pipes, which spew fire. Then, Mario passes under two Thwomps.
Then, Mario uses a Sling Star and is shot into oblivion. Yeah.

You know, when your Sling Star sends Mario rocketing through the sky like Team Rocket (nailed it), that's a sign that maybe the star shouldn't have 50 speed.
Just to see, I changed the star's speed to 30 and it worked much better and did not fling Mario into the cloudy void.

You walk for a bit on some blocks activated by a switch randomly floating in the air to get a Shine Sprite.
You activate this Shrine Sprite by collecting five red coins, all of which are in the same place underneath the randomly floating switch...

The point of red coins is to make Mario look for them. You might as well just delete those coins...

So after a bit of easily walking through an obstacle free hall of switch blocks that take more than enough time to go away, you get to a sign that reads:
"Bowser : Mwahahaha! Mario! If you want to get the shine sprite. go to my trap. if you don't want to trap. don't get the shine sprite."

That raises more questions than it answers: For one, how is that Shine Sprite in any way a trap? Also, why is Bowser doing this? Why is Mario here, for that matter?

The players will have questions, and you'll have to answer them if you're doing a story-based level. After you read the sign, you get the Shine Sprite.

The level is far too short for a whole episode: sign, Goombas, locked doors, fire pipes, Thwomps, sling star, switch blocks, Shine. That's it, in its entirety.
This is episode 1 of a series: you need to establish the premise and explain what's going on.
I don't know why any of the characters are here, why they're doing what they're doing, or what the underlying premise or idea is. You need to establish these things.

So, this level gets 1/5. Way too short and easy to be fun; you might as well just give Mario the Shine.

How to fix it: Make the level longer, add more obstacles, actually playtest your levels, and answer the questions players may have while playing your level.