After deciding upon a theme for the character and enemy sprites with the artist, I decided to use a stylized jungle temple environment.  The foreground tiles were influenced by the simplicity of Super Mario Bros. 3 cavern tilesets.  Though time consuming, I added the fake isometric view to the add depth to the environment.

I included coins originally as part of a health system. When I removed a health system, choosing to rather simply restart the player at the beginning of a level each time they failed, I kept the coins. In play-testing, I found that despite the coins not giving the player anything, players still wanted to collect them all and they drew the player through the critical path. The above screenshot is of a Mario-inspired secret room filled with coins.