This is a fairly simple hack, which keeps the original level design from New Super Mario Bros, but makes the game much more challenging. I'm sure most people would agree that NSMB was rather on the easy side, so this hack is basically designed to add another playthrough for people who are looking for more of a challenge.

ALL levels complete!
http://nsmbhd.net/file/rMZU6PT6qfHAraKo/NSMB2ndQuest_v08.zip

So what is changed?
- More enemies
- Less powerups
- Crazy boss battles
- The two secret worlds (4 & 7) offer an even tougher difficulty level that even the most hardened Mario veterans will struggle to complete.