Really nice looking level in terms of aesthetics. Though now that I come to think about it, the moon coin graphics could use the animated colours from palette 6. Also the ice spikes just doesn't fit with the environment; they look a bit too realistic. I think it's just me though
In the level itself, it seems that the Ice Bro.s iceballs melt the frozen coins? And make a coin sound effect when it lands? I suggest you change that.
For the sub-area with the moon coin, I would prefer the moon coin come in with a poof instead of suddenly appearing.
I can clearly see a junk map16 tile next to the semisolid at 0:07. Probably just a mistake. And there is a bizarre glitch at 0:59 where the penguin clips through the slope. I guess this patch
would fix it? Plus the spiky balls the piranha plants are blowing have their colours a bit messed up. You could change that into a more red, green or black colour.
The level before the checkpoint also felt kinda short to me, so if could add more level, that would be nice. Other than those, I wasn't able to find any glaring issues.