The 3-3 map corruption trick uses the tongue glitch to rearrange the objects in the level to allow you to reach the second middle-ring from the second screen, to skip the submarine section. You need either a POW block or a big egg to do it. Big eggs are recommended, as there is no known way to consistently get a POW block.
How To Do It
Once you reach 3-3 with the big egg, go to the 2nd screen:
- Grab any enemy, throw the big egg into the air and spit out the enemy right before the big egg lands. This will activate the first phase of the tongue glitch where Yoshi both has and does not have something in his mouth.
- Next, go to where the Shy Guys are on the red bridge, tongue and get hit when Yoshi's tongue is fully extended. This will activate the second phase of the tongue glitch and turn Yoshi and Baby Mario invisible as a result.
- Reclaim Baby Mario and do a full jump followed by 3 flutters to enter the helicopter bubble.
- Once you transform into the helicopter, the map should be rearranged, allowing you to fly to the right and enter the middle-ring.
- After you get the middle-ring, hold down to die and then respawn. You have now successfully skipped the submarine room.  
The following images will show you what good and bad positioning of the big egg looks like.
Remember, that if the big egg is too far off-screen, it will despawn.
|Big Egg Baxter Visual Cues|