If you manage to get going faster than maximum running speed, you don't accelerate back down to maximum speed. There are two main ways higher-than-maximum speed is achieved:

1. Get on top of a top-screen block When you get on top of a block that is on the top of the screen and try to move towards the center of the block, it will push you the other way at high speed. So if you are on the right side of a top-screen block and tap left, it will launch you to the right at high speed. If you then immediately hold right, you will maintain this speed until you stop holding right or hit a block. If there are multiple top-screen blocks in a row and you get on one that isn't on the edge, you will get trapped between the two surrounding blocks. To launch off, you can simply jump and move slightly to one side before trying to launch.

Launching off of top-screen blocks is useful on Level 1, and can be used in Level 2 as well, but is very hard.

2. Crouch-jump into a block If there is a floating block and you are Big Mario/Luigi or Fire Mario/Luigi, you can use it to launch yourself. To do this, crouch and jump into the block, and stop crouching so that Mario/Luigi's head gets placed inside the block. Then, just as with top-screen blocks, trying to move towards its center will launch you the other way. It is possible to get a crouch-jump boost off of a block that is high enough without bumping the block. This means that you can boost without falling back down immediately, and boost off of breakable blocks.

Crouch-jumping into blocks is useful in practically every level.