My first level!
It is relatively easy to clear, but more difficult to get the red coins. Red coins are optional
NJ5-GJF-JLF
I'm a person who enjoys traditional levels, so I think I might be the target audience for your course? I agree with almost everything Gendo said, though. (The one point I disagree on is that I think Hammer Bros are fine when used carefully. More on using enemies carefully in a bit.)
I'm not terrible at Mario and neither am I an expert speedrunner. I would not call this level easy to clear. I finally got to the final Thwomp/Lava Bubble/cannon area and died (again) there. So I'm giving up for now. (
EDIT: I followed scott_pilgrim's advice and got the Fire Flower and was able to beat it with invincibility frames. Not ideal, but at least I've cleared it. I'd ignored the Fire Flower before because it didn't seem worth the risk, but it wasn't actually that hard to get once I tried.)
I'm not entirely sure who your target audience is, but I'm going forward with the assumption that it's people who like traditional levels. So I'll give some specific feedback based on that assumption. And I'm mostly just going to address the path to the goal, not the red coin paths, since I only tried a few of those and didn't make it to the end of any of them.
First, you use two or three enemies in places where one would do. This is basically ubiquitous throughout the level. Like the very first Koopas, you only need the top red one. The other ones are just clutter. Every block that has two Spike Tops probably only needs one. That spot near the end has two Dry Bones, which is great for keeping players on their toes while trying to figure out when to approach the Hammer Bro, but one would do the job. And maybe just one giant Lava Bubble at the end between the Thwomps.
The level lacks a feeling of cohesion. There are lots of types on enemies, most of which you only see once. It makes the level feel thrown together, even though it's obvious you put some work into it. Since a lot of the enemies in this level just serve to be general obstacles, you could replace many of them with one type. Dry Bones, perhaps. The Koopas and Goombas could all by Dry Bones and the level would play similarly. That would be one possible step toward giving the level a theme of sorts.
I would avoid challenges that require you to be small Mario. (Again I'm assuming you're trying to make a challenging traditional level.) There's a spot in the snake block room where you can't get through the spikes as Super Mario, for instance.
I would either only point arrows toward the goal or only toward red coins. Right now they seem to be a weird mix of both, making for inconsistent leading. And on a tangent, I would include more regular coins just for getting. Nice to have some coins in a level.
Still on the topic of coins, I recommend against putting 10-coin blocks in levels unless they fill a specific purpose. When placed randomly into a level, they're boring time-wasters that some players will nevertheless feel compelled to collect. I mean if they're playing Endless Challenge mode or whatever, they may need those coins. So they'll jump up to where the giant Spike is, probably take it out, and then spend several seconds collecting 30 coins from those three blocks. And then they'll die and have to do it again. If I'm putting a 10-coin block in my level, it's for one of three reasons. First, it can be fun if it's a challenge to actually collect all ten coins. This means either there's a persistent hazard, some tricky platforming, or auto-scroll. Your giant Spike maybe works that way once, but on subsequent attempts it's obvious they should take it out first. Second, I may place a 10-coin block if there's an unavoidable lull in gameplay (usually in an auto-scroll level, but maybe due to moving platforms or something) and I want to give the player
something to do while they wait. Third, they can be useful if I want to make the player stay in one spot for a couple seconds. If it's an auto-scroll level, I might want to keep the player from hugging the right side of the screen and getting killed by an enemy that spawns there. I also have one at the start of the third part of my Chomp Cavern level in hopes that the player will look at what's in front of them before rushing in, but I think I may take that one out. Anyway this wall of text is just my personal guidelines for 10-coin blocks, and not hard-and-fast rules. I'll still include the occasional 10-coins in a regular brick block just as a cool surprise for curious players, though even then I want some threats nearby to keep them on their toes.
I guess this sort of turned into a 10-coin block treatise. Anyway, I really highly recommend going through all the Yamamura's Dojo tutorial things if you do want to make some traditional levels. I consider myself a reasonably good course designer, but I still learned a lot from them. One standout thing I learned was making your power-ups matter in order to make them more fun. In my first version of Piranha Pirates on the Wii U Mario Maker, I had Super Leaves instead of Fire Flowers because I thought the Fire Flowers would make taking out the Piranha Plants too easy. But after watching the video, I changed them because (1) fireballing Piranha Plants is fun and (2) the level is challenging enough even with that power-up. If you want something more engaging, you could watch some YouTube videos on the subject of Mario Maker course design.
