I'm really happy to do my first walkthrough of all time! I hope this expands to other parts of vizzed, because this, is a DS game!
I didn't succeed in getting 9,999,950, here's my final score 9,089,750.
Walkthrough started on 2/14/12! Edit: I should've put this in walkthroughs of video games, darn. Can someone please move this to walkthroughs in video games?

By Super Mario Bros 2 Japan, do you mean the one that's called Lost Levels here in the US?

Both games I could never beat, so I guess it'd be nice to see a walkthrough on one of them. x3

Thats awesome! Im also currently trying to make let's plays/ Walkthroughs! Anyways i still need equipment to record. Can you give me some tips? My youtube account Is MinkNyu same as my User name Haha.

Someone70 : I am meaning the lost levels, the walkthroughs won't be done, I can't beat the US Mario 2, but I can beat the JPN Mario 2.
MinkNyu : Well you came to the right place!
World 1-1: There's a mushroom in the 2nd ? block of the level, get it, and go right until the lonely ? block, hit it, and you can go through the rest of the level being able to get 2/3 star coins, above one of the blocks is a vine, which you'll find coins and a 1up! The 1st star coin is really easy, just jump to the top of the pipe. Keep going right until near the pipe, there's a vine in one of the 3 blocks, above the 3 INVISIBLE blocks. Go down the pipe to get the 2nd star coin, with a mushroom, if you take the pipe, you'll come out right after the 3rd coin, you need super Mario to make a ground pound on the blocks (press the down d-pad while in the air or on the ground to crouch.) After that is a koopa and a staircase (1-up reference), must be fire Mario, stomp the koopa but don't kick or burn it, instead, carry it to the staircase, the middle step in the staircase is good, wait until it hits you and makes you turn to super Mario, jump on the koopa at the right time, get 99 1-ups!, get the flag and your done with 1-1 100%!
This walkthrough won't cover all the levels though, continued in the next post or edit, any questions? Or are you ready for world 1-2?

Spaces between post will be 2 or 3 days, so be patient.

Sorry to bust your bubble, but it is impossible to get a 9,999,990 score on Super Mario Bros 2 JPN (Lost Levels USA). All actions that give points are multiples of 100. The action you can do that gives the least amount of points is breaking a normal brick, which is 50 points. So the highest score you can get is 9,999,950. I know because I have the high score for that game in the competition. If you try to go higher than that, the score resets to 0. So if you find yourself at 9,999,950, don't try to do something thinking it will just max out the points. It will reset it.

Super Mario bros 1 and lost levels can't have a 8th digit, which means (what you said) the score rolls over and displays 0,000,000 if you roll the score once, but this is a weird score system. Most NES games can't even hold 7 digits! I have done a score rollover successful run when getting star number 2, I had 98 lives when I finished, and I had almost 260k points before the 1-up tally.
You're right with the 9,999,950 being max. My highest alltime score was 10,058,450! My little thread bubble was popped, but the water was controlled by a wii remote, and it reformed!

Now, World 1-2!
You'll start the level automatically groundpounding blocks to get 9 coins, go all the way right, until you get to a star coin, grab it, and keep going until the next star coin, kick the koopa (not me) and it'll grab the coin for you, go right even more until a bridge comes on screen, stand on it so it becomes 3/4 straight, then run up and jump at the right time to find the star coin and a shortcut to world 1-MCASTLE
otherwise, go to the regular pipe and you get to world 1-3!

Spacing is extended to 3-5 days because I'm losing focus on this.
So easy so far, 100%

World 1-3: go to a big spring, stand on it, hit A, you bounce really high! Bounce on the spring, find the next spring, bounce, then on the mushroom with A, first star coin way above the mushroom.
Fly down and go right until you see the 2nd coin, then go right until the 3rd coin, and go for the flagpole! The higher you are on the flag, the better the award is, 100, 400, 800, 1000, 2000, 5000, 8000, then 1-up!

World 1-mini: tommorow.