Summarize this article:

If this is done correctly, you can keep jumping on it to build the points.    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/3\/3c\/Get-99-Lives-in-New-Super-Mario-Bros-DS-Step-4-Version-2.jpg\/v4-460px-Get-99-Lives-in-New-Super-Mario-Bros-DS-Step-4-Version-2.jpg","bigUrl":"\/images\/thumb\/3\/3c\/Get-99-Lives-in-New-Super-Mario-Bros-DS-Step-4-Version-2.jpg\/aid388967-v4-728px-Get-99-Lives-in-New-Super-Mario-Bros-DS-Step-4-Version-2.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/en.wikipedia.org\/wiki\/Fair_use\">Fair Use<\/a> (screenshot)<br>\n<\/p><\/div>"} After you build the points as high as it can go, it will start to give you one-ups.   You should be able to take your hands off the DS and watch your lives go up. You can get up to 99 lives. Keep in mind that you may lose lives through time out.    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/f\/f9\/Get-99-Lives-in-New-Super-Mario-Bros-DS-Step-6-Version-2.jpg\/v4-460px-Get-99-Lives-in-New-Super-Mario-Bros-DS-Step-6-Version-2.jpg","bigUrl":"\/images\/thumb\/f\/f9\/Get-99-Lives-in-New-Super-Mario-Bros-DS-Step-6-Version-2.jpg\/aid388967-v4-728px-Get-99-Lives-in-New-Super-Mario-Bros-DS-Step-6-Version-2.jpg","smallWidth":460,"smallHeight":345,"bigWidth":"728","bigHeight":"546","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/en.wikipedia.org\/wiki\/Fair_use\">Fair Use<\/a> (screenshot)<br>\n<\/p><\/div>"}

Summary:
Go to level 2-4. Finish the level like you would do normally, except when you get near the flag at the end, there should be a Koopa Troopa coming down the stairs. Jump on it as it is coming down the third to last stair. Finished.