When the Going Gets Tough
From the Super Mario Wiki
The first part of the level features an arena with a dramatic decrease in height. It features a few Smashers at the beginning, though two Ziggies and Hoppers each appear at the end, behind no particular cover.
The second part of the level features another arena with a dramatic decrease in height. A few Ziggies appear at the beginning of the area, though more spawn periodically. Mario and co. must reach the area shaded in yellow to complete the level.