World 5-1 (Super Mario Bros. 2)
From the Super Mario Wiki
This level starts with the player staying for very little in the outside, as the rest of the stage takes place underground. There is an extremely long waterfall that can initially be passed through the falling wooden platforms, then by jumping from Trouter to Trouter. The timings are strict, and it is advised to play as Luigi or Princess Toadstool only (and either of them must land on at least one of the Trouters before performing the larger jump, as it by itself is not enough to overcome the chasms). This is the first level in the game where the completely fire-shooting Green Birdo is fought.