So, the final level, eh? This is separated in 3 segments.
You have to defeat Bowser with Minny Mario on the last level of world 5.
Although there are 150 stars in total, you only need 80 stars (and Mario) to complete the game as this is the number of stars you need to get into the final Bowser level.
For New Super Mario Bros., You reach level 7 by defeating the level 5 final boss (Petey Piranha as mini Mario
you have to beat the entire game as mario and luigi. get a gold flag on every level as mario or luigi collect all star coins
There are 9 Worlds in total. To get World 9 you have to beat the last level of World 8 which is Bowser's Castle.
There is no game called Super Mario 63. There is one called Super Mario 64. On the final level of it you have to fight and defeat Bowser.
To the final Bowser level, Bowser in the Sky.
To get the star Rank, you have to get to level 40 with Mario and Luigi. Your reward is the Excellent! Badge. To get the Final Rank for Bowser, you have to get to level 40 with Bowser. Your reward is the Intruder Fangs. They let you take two turns in a row. Hope I helped!
The final "new" course is Rainbow Road, and the final "retro" course is N64 Bowser's Castle.
Sadly Mario, Luigi or Bowser wont level up after you beat the final boss (Dark Bowser). After you beat Dark Bowser the game will reset to the spot from where you turned it on. An easy way to level up Mario and Luigi is to fight enemies over and over in the airway. I dont know for sure how to level up Bowser but is has something to do with using The Broggy Bonker attack. I would save before you fight Dark Bowser so your levels wont reset. Good luck with Dark Bowser.
The final level in world 8 is bowser's final castle. You have to battle Bowser AND Bowser junior at the same time. Once you beat them, you will have saved Peach and on the bottom screen it will show you how to be Luigi. (Press L+R+A at the file loading menu to play as Luigi.)
The nefarious 'Shadow Mario' is none other than Bowser Jr., Bowser's son . Bowser convinced his son that Peach is his mother and that Mario is the, as Bowser Jr. himself said, 'bad guy'. So Bowser Jr. kidnaps Peach, all the while smearing good name of Mario by making it look like he (Mario) was responsible for all of the graffitti and the dissappearance of the shine sprites.
in the last level
level 12
40.
Beat bowser, and huge bowser on the last level.
After the game ends, you still have some things to do. You can collect all the Special Attacks for both Bowser and the Mario Bros. and you can level up too. If you have all the Special Attacks and reach level 40, you'll reach Rainbow Rank with Mario and Luigi and Final Boss Rank with Bowser. This will give you a new badge for the Bros, and two powerful items for Bowser. Other than that, you can test how good you are on the Challenge Node with Mario and Luigi (inside Bowser), and your skill with Bowser's Special attacks with Madame Broque on Bubble Lake.