Without the rigid restrictions of tile-based sprites and backgrounds, the designers were free to explore new gameplay mechanics. When Mario lands on top of a tree, it teeters over and eventually falls if he is stationary for too long. Mario can also swing on ropes and walk on wires that bend and stretch under his weight. Early in the game's development, the developers planned not to use voice acting for the game to stay true to the spirit of Super Mario Bros.; however, voice acting was eventually embraced by the developers, who decided that it would serve the game in a positive manner. Although voice acting was used in earlier 2D Mario remakes, New Super Mario Bros. is the first original 2D Mario game to use voice acting. Charles Martinet returned to voice Mario and Luigi, along with Nicole Mills as Princess Peach and Dolores Rogers as Bowser Jr. New Super Mario Bros. features original music composed by Asuka Ohta and Hajime Wakai under the direction of the Super Mario Bros. series composer, Koji Kondo, who also created the "Aboveground BGM", the main theme for regular levels. The game's music dictates gameplay; enemies jump and dance in time to the music. Predicting enemy movements, players can time their jumps with enemy movements to reach otherwise inaccessible areas. Reception New Super Mario Bros. was released by Nintendo in North America on May 15, 2006, in Japan on May 25, 2006, and in Europe on June 30, 2006. Nintendo did not specify why it chose to delay the game's release in its home market of Japan by ten days, but GameSpot noted that "it stands to reason that the company simply wants a few more days to build inventory." In Japan, over 480,000 units of New Super Mario Bros. were sold on the day it was released and 900,000 copies in the first four days. At the time, it was the best-selling debut for a Nintendo DS game in Japan, but it has since been surpassed by Pokémon Diamond and Pearl. It is Japan's 26th best-selling game in 2008. In the United States, 500,000 copies of New Super Mario Bros. were sold in the first 35 days, and one million copies were sold twelve weeks after its release. Worldwide sales have steadily increased throughout the years, with five million copies by April 2008, eighteen million by March 2009, and 30.8 million by