How many star coins are there in Super Mario 3D land?
Solution 1:
There are 285 Star Coins in the normal levels and 50 Star Coins in the bonus levels.
However, since StreetPassing with other players allows you to "reset" mystery boxes, letting you collect their Star Coins again, potentially there's an infinite amount of Star Coins, however you can only accumulate up to 999 star coins
In any case, you'll need only 290 Star Coins to unlock every level.