Tip: You can use Lunar Magic's Overworld Layer 3 Editing system to edit or create your own layer 3 images (castle bricks, fish, rocks) and apply unique effects per level via the Layer 3 Bypass in the main editor.
The song that plays in MM2 levels with the SMB1 Forest theme. One of my personal favorite remixes from Mario Maker 2. This port has a version with echo as well. The instructions to enabling the echo is in the .txt file.
I'd imagine this theme being played in World 4-1 of Super Mario Bros. A clearing with a path through thick trees with the Lakitu throwing down Spinies to block your way. Though it would only be for 4-1. Same would be for 4-1 and 4-2 for the Lost Levels.