In Super Mario Bros. 2, you get these potions. Which you can toss down to make doors. Go through the doors and you find all kinds of stuff, but probably one of the more important changes is that the plants that hold vegetables now hold coins. Coins that you use at the end of the stages to gamble for extra lives.

Now, if you try to get coins more than twice in a level, you start picking up vegetables instead of coins, probably to prevent you from abusing the system.

But, what happens if you go to, say, 5-1?

You notice how the potion is near some plants and a pit?

Grab the potion, toss it down, and go into Subspace. Grab the coins and while you're in subspace, jump down the hole.

It'll cost you a life, but you gain five coins (six if you're quick). Then, do it all again, grab the coins and jump down the hole. As long as you don't actually exit to the 'real world', then it doesn't count toward your two-trip limit.

Once you have all the coins you want, go on to the end of the stage. Then check out your coin total.

Depending on how many lives you sacrificed for the coins, you might be here for a while using the slot machine.

Enjoy!