Speaking of level design...
A few things you should think about:
Bros so early in the game? No.
And the part with the Shell Bro and the Multi-Coin Block is aimless - trying to catch a shell for a few minutes to use on the coin block is tedious - there's no point of having to go through that and to find only coins that you can even get to collect since it takes time to catch and throw the shell again and again.
To many spikes too early - cut down on them.
The giant pits aren't a great idea for a first world - with little room to jump.
And there are many more, but these are the ones I can only think of.
A few things you should think about:
Bros so early in the game? No.
And the part with the Shell Bro and the Multi-Coin Block is aimless - trying to catch a shell for a few minutes to use on the coin block is tedious - there's no point of having to go through that and to find only coins that you can even get to collect since it takes time to catch and throw the shell again and again.
To many spikes too early - cut down on them.
The giant pits aren't a great idea for a first world - with little room to jump.
And there are many more, but these are the ones I can only think of.