1-2 Any%

Basics

The major notable trick in this level is referred to as the "1-2 skip," which entirely bypasses the second screen of 1-2
Though very precise, the trick is easily attempted multiple times in succession and can be grasped by a new player with a little bit of practice.
The recommended method for performing this trick involves spitting a flower enemy (Crayzee Dayzee) into the wall and bouncing off of it as shown in the GIF.
After landing 1-2 skip, you go a bit to the left so you can have right momentum when you clear the wall.
You have to jump over the second pit or you will fall in and lose time.
Be sure to have an extra egg to shoot the pihranha plant near the end, saving a bit of time not collecting the red coins.

Spit Method

There is a small optimization that can be made which requires a perfect jump chained with an extended flutter to skip the beanstalk. It can be seen in the Individual Level World Record.
You upspit the enemy without holding right so it lands in the correct position, bounce off of it to buffer an extended flutter, then perfect jump off of the rotating platform.

If you miss it, you can get up using this backup involving a perfect flutter (hold B when you bounce off the enemy to bounce higher).