Light skip

There are a few ways to setup the spring, this is the best way I've found so far.
Mario jumps on the bottom-left corner of the spring.
Both babies jump onto the very left side of the spring.
Press B (or A).
Now the hard part - hold down and press A, very soon (7-10 frames) after press X. If the babies did not take the spring, you did it correctly.
Hit the ! block and roll into the spike pit.
Just before rolling into the spike pit, press X.
After getting hit by the spikes, start holding right. You need hold right for the rest of the trick.
When you see Mario bounce to the right after getting hit by spikes, start spamming A. Depending on your timing, he might fall in the spikes once or twice more before this.
After Mario flies back to the left, listen for 5 jumps. After the 5th jump, stop spamming A, but keep holding right. You should enter the loading zone.
Then hit the ! block, go to the right and hit the pipe block, then step on the blue switch.