Sunken Shinra Plane

Go to the bay near Gold Saucer, there is a dock nearby. Submerge and you’ll see a plane on the sea bed. Touch it to enter. The enemies in here are very hard, so be careful in random battles. Go left and save. Take the Heaven’s Cloud from the chest and go in the door to the north. Go left and get the Escort Guard from the chest. Go to the top right corner and pick up the Double Cut materia. Go to the top left corner and take the Conformer, Yuffie’s Ultimate Weapon. Then go back to the entrance and go north across the beams and pick up the Megalixer in the chest. Then go back to the Save Point. Go left and you’ll meet Reno and Rude again. You’ll have to fight them once again…

Reno and Rude

This is much like any other time you have faced Reno and Rude, hurt one enough the other will go, Rude can use Fire and Ice, and Reno uses Neo Turk Light a lot. Haste your guys, Barrier etc, or just use KOTR to kill them in one go. They can confuse you as well, and use Summons whenever you can. You’ll get an Elixer when they leave.
Go through the door they were by. Take the Megalixer from the chest and go all the way along the walkway to get to a cheat with the Spirit Lance in. Go down to the lower level and take the Outsider and Cid’s Level 4 Limit Break Manual, Highwind from the chest below. Go to the helicopter and pick up the Summon Hades materia there. There’s nothing else here so you can leave or morph the enemies here into various sources.

If you completed the mini game, you need to get the Huge Materia from the downed Shinra sub so go to the islands to the south of the World Map, west of the Temple of the Ancients, and south east of the weapon smiths house. Submerge and look around underwater for the red sub. Touch it to pick up the Huge Materia.

If you didn’t complete the mini game go back to Junon and to back to the grey walkway in the centre of the town. Go down the elevator to where the dog is, fight some guards then examine the dog, follow him and examine him again. Pick the top option. Fight the guards that show up, then choose to either fight the commander or not. You will then gain control of the sub.

Now go to the southern part of the Northern continent. Look around for a tunnel in the wall leading to a cave, there is a spiky object here. Touch it to take it. Now you can choose to go back to Junon. You can go back to airport to see an optional FMV of the plane taking off with the Huge Materia. Now go back to Rocket Town.