OK then, let me review this level.
Level design: 4.5/10
This was quite a nice SMB3 run, and very fitting for a world 1 level, even if it's a little on the short side. The added level timer with Lua helped to keep the player moving through the level, even though it lasted too long for a moderately short level and ticks quite slowly, so the player's bound to complete it in less than half the time anyway. The bonus areas added throughout the level provided something to look out for and provided a sense of reward for locating them, and the level, despite being a world 1 level, has enough variety that justifies its level 3 location very well, such as the moving platforms, and added water pits which are, fortunately enough, small enough to not get trapped in. Unfortunately, this level appears to be tripped up by its own design. If you fell from one of the moving platforms towards the end of the level, you would have a lot of backtracking to do, which can cost a life if the level's timer runs too low. The bonus areas, while a neat concept, were quite flat and barren and didn't really have much in there that provided a sense of reward, especially the second one which was nothing but coins. However, it can prove useful in the episode's context because you can rack up some useful lives.
Graphics and music: 5.1/10
While the SMB3 athletic theme fits with the overall theme of the level, with the very active platforming further enhanced by the level timer, there's a missing music file that's supposed to play in the bonus rooms. You may want to consider adding that in. As for the graphics, I must applaud you for taking a level that predominantly uses vanilla graphics and still manage to make it look good. As well as this, every graphic fits in with the style of the level so nothing looks too out-of-place - vanilla SMB3 NPCs and that abound this level. With this being said, the level is very well decorated, even though the bonus areas are flat, as mentioned earlier, but they're also really barren to boot. While this is the start of the graphical cons, I managed to capture two graphically-jarring flaws in one screenshot.
First of all, thanks to the jagged grass tileset, there's a cut-off on the bottom of the pipes which is rather unsightly. Making one of the pipe blocks a BGO and placing it under the pipe will easily fix this issue. Another thing is the weird transition into the inside grass graphics because there aren't any sideways tiles to go with it - these can help ease the transition. Also, as Cheeyev pointed out earlier, a jarring graphical change is seen in the second bonus area in the clouds, where it suddenly switches to SMB1 style as opposed to the overall SMB3 style. Keep the SMB3 style in there for consistency is what I would say.
NPC placement: 5.3/10
First and foremost, there are way too many powerups in the level, and some rather powerful ones are given away for free in the bonus sections - you might want to limit the amount you give away for free. Also, while coins are relatively abundant in the level, they seem to be packed in certain locations, while in others they're very hard to find. In particular, there's too many coins in the SMB1 bonus area, but not just that, but they appear to have been just plonked here and there without any thought, as some of the coins are difficult or even impossible to obtain because they're too high up. As the trade-off, there are many locations in the main area where coins are lacking, making them quite sparse. Speaking of coins, it's worth mentioning that there's a random Blue Coin in a bubble that does nothing and looks out-of-place, along with the fact that it's quite hard to get, so I would suggest getting rid of it. Anyway, I've talked too much in this section and I still haven't got to the enemies. Their placements here were much better, and in keeping true to its name, Goombas are the main focus of this level, although there isn't really a lot of variety because of this, but then again it doesn't really matter.
Overall result: 5/10
It's a good world 1 level, but still with its flaws, like the pipe cutoffs and empty bonus sections. By fixing them, you should be off and away!