World 2-1

Two coins were added inside the pipes, which made the entire coin formation symmetrical.

World 2-3

Five brick blocks were removed from the right side of the half-pyramid at the end of 2-3.

Consequently, a shell will clear out the blocks a tad faster, but it won't hit one of the coin blocks on the right wall. The three blocks behind the pipe were removed to prevent Mario from getting stuck if you slide through the pipe.

World 2-4

The division between the top and bottom section was extended downward by two blocks so that we can still see the brick block at the top left.

Here's where the extra ceiling ends in SMA4.

World 2-Pyramid

A nice touch here in SMA4, the left wall at the goal area is now the other side of the pyramid started at the entrance.

Go up and left to find a P-Switch that makes 20 silver coins appear for a short time.

World 2-Airship

The first section of the rope handrail was removed.