i dont think the mini-games are true wifi. as in you can't play with someone in california if i am in chicago. but if you have 4 friends over with ds's you can play.
I beat the game last night. I thought this is child's play compared to the original Super Mario Bros. I unlocked world 4 by beating the world 2 boss as mini mario. I've been trying to unlock world 7. To do this, you need to once again play as mini mario and go into the ghost house. To the far right of the 2nd red button, instead of going into the tube, you'll have to "bounce jump" up the wall and to the ledge on the upper right hand corner. There's just 1 catch: the damn ghost that's chasing you around. I will try again tonight.
I don't know if you played "Lost Levels" from way back, which was supposed to be Mario 2 in Japan, but not released in the US until much later and titled differently because it was "Too hard for Americans". Anyway it was much, much harder than the original Mario Bros. I suggest you try it out if you're looking for a challenge. I have beat it twice personally, but don't dare put myself through that punishment again, bring your patience, you'll need as much as you can muster!
use a small mushroom to become mini mario, then beat the bosses in world 2 and 5 castles to go to world 4 and 7
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There are two ways to "save" the game in NSMB. The 1st one is soft safe, which can be accomplished w/ all DS games by simply closing the DS. The 2nd is using your special coins to open a route to a mushroom house, which will cause a save screen to pop up.
NSMB is very short compared to the 2 games you mentioned. I think it took me roughly 8 hours to beat NSMB.
For more details on unlocking world 5 and 7, check out IGN's NSMB guide.
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