New Super Mario Bros. 2/Coins

Coin farming
The best way to gather coins in New Super Mario Bros. 2 is the Coin Rush mode. In that mode, with the right combination of skills and luck, it is possible to get up to 30,000 coins in a single Rush of three levels.

That said, if you'd prefer, there are a number of ways to make a large amount of coins in the main game. Although these methods will take more time than Coin Rush, they require less luck and skill, and thus might be simpler for the average player.

World 1 - 1
For the most part, Stage 1-1 is a simple affair, in which you can get hundreds of coins from playing well, but nothing special. All this changes when equipped with a Gold Flower. The final goomba tower of the stage is worth 250 coins if hit by a blast from the flower. This is a hefty sum, especially when combined with an extra 30 coins from the nearby tower you also have to encounter. Even better, you can go back a distance to the pipe that sends you into the sky, leave the area, and come back immediately to respawn the tower. Using this strategy, you can manage to pull off the trick quite a few times, easily netting over 6,000 coins before the clock runs out.

World 1 - A
This is a great level for getting coins, with various factors making it easy to get in the 500 to 1000 range. There are several tricks throughout the level for getting a lot of coins.

Just before the midpoint flag, wall jump up above the pipes and move to the left. You'll find a secret passage going right. You'll find a gold ring, a koopa, and some goombas. Go in the ring, grab the koopa, and shoot it along the line of goombas to get over 100 coins. There is a similar setup a bit right, except there is also a block at the end that will eventually spew up coins. Furthermore, above this is yet another block, which can become a gold block. In total, this diversion can net north of 500 coins if all things go well.

Near the end of the level, there is a piranha plant coming out of the ground. Head into its pipe to enter a cave with a gold ring, a koopa, and several more plants. Quickly go through the ring, jump on and pick up the koopa, and throw it over the plants to destroy them all. This will create coins for each plant destroyed, leave a trail of coins in the shell's wake, and make coins spew out of the pipes. Although a bit tricky, this method can get over 100 coins.

World 2 - Rainbow
In of itself, World 2's Rainbow stage isn't that impressive. You can get 200 or so coins, but it won't really pay off unless you go through the red ring that appears and collect the eight Red Coins. This creates a Gold Flower, which is then put into your inventory. You can then use this Gold Flower for almost ANY level in the game.

Coin milestones
New Super Mario Bros. 2 keeps track of how many coins the player has collected. Every so often, it will display a special notice celebrating a milestone. The player is rewarded for reaching the 1,000,000 coin mark. The following is a list of those milestones.

Milestones

 * 500
 * 1,000
 * 2,000
 * 3,000
 * 5,000
 * 10,000
 * 15,000
 * 20,000
 * 25,000
 * 30,000
 * 35,000
 * 40,000
 * 45,000
 * 50,000
 * 60,000
 * 700,000

Coin rush
Coin Rush is possibly the biggest innovation of New Super Mario Bros. 2. In this mode, players must play through a series of three levels from the main game, collecting as many coins as possible.

Rules

 * Coin Rush is unlocked at the end of World 1.
 * Players must beat a Coin Rush without losing a single life.
 * 1-Up Mushrooms are replaced by Golden Mushrooms, which give 50 coins.
 * By default, the time limit is only 100 seconds..
 * Time limits can be extended by reaching the midpoint flag or by collecting clocks.
 * Remaining time will also be converted into coins, at a rate of 1 coin for every 5 remaining seconds.
 * Star Coins grant 10 coins for the first one, 20 for the second, and 50 for the third collected in a level.
 * The third random course will always be a Tower or a Castle.
 * Reaching the top of a flagpole will double one's coin count. This effect is cumulative, meaning that the first stage's coin count can be multiplied by up to 8 times.
 * Once players beat World 6's Castle in the main game, they will be given a Gold Flower in the Item box, so long as they play without the White Raccoon suit.
 * A maximum of 30,000 coins can be collected in a single Coin Rush, or 3% of the 1,000,000 coin milestone.

Packs

 * Mushroom - Selects three levels from Worlds 1, 2, and Mushroom
 * Flower - Selects three levels from Worlds 3, 4, and Flower
 * Star - Selects three levels from Worlds 5, 6, and Star

Streetpass
Upon the completion of a Coin Rush, players are allowed to save a record of their run. StreetPass exchanges this record with other players. Beating another player's record on the same Coin Rush grants an extra 1,000 coins.

Only one record can be saved at a time.

Rainbow Stages
Rainbow Stages are special stages that are only unlocked for one use, and thus need to be unlocked again every time they're played through. Rainbow stages are notable for having no enemies and a large number of coins. To unlock a Rainbow Stage, players must reach the flagpole at the end of another stage with a certain amount of time on the clock left. The amount differs depending on the world in question.

World 1 - Timer ends with the number 11 World 2 - Timer ends with the number 22 World 3 - Timer ends with the number 33 World 4 - Timer ends with the number 44 World 5 - Timer ends with the number 55 World 6 - Timer ends with the number 66 World Mushroom - Timer ends with the number 77 World Flower - Timer ends with the number 88 World Star - Timer ends with the number 99