Also, relating to difficult it's interesting that the original game that SMB2 in the U.S. was based on didn't have the B-run ability, and that change made the game substantially easier. Though in that case they may have decided they had to add it in order to be consistent to SMB1, and the decrease in difficulty was just an unintended side-effect. (Also, not having a save feature made the U.S. version a lot harder, so maybe that balances out with adding the run ability.)
