Once you have defeated him grab the Potion in the top right hand corner and then continue through the sewer. Captain Obvious says: don’t forget to pick up the Steal Materia sitting on the ground along the pathway. Jump down the hole at the edge of the screen. Continue through the sewer until you reach the train graveyard.
There is a Hi-Potion in the barrel through the first train and another on the roof of the train. Continue across the roof onto the next train and scale down the beam lying across the end of the train. North is a barrel with an Echo Screen in it. Make your way right and into the train on the right to grab the potion on the ground. Continue through the train car and take a right. Jump up the ladder off to the right. The ladder down is just up ahead. After you climb down go north again into the car and continue north into the next screen.
There’s a Potion at the bottom left hand portion of the screen and a barrel with some loot in it. Jump in the train engine and force the train forward. Pull it back again after you jump out. Go around the engine and grab the potion on the top of the car. Hop in the other train engine and pull it backwards, then crawl back up the ladder and jump across the top of the engine heading left to finally get out of the train graveyard.
Sector 7 Pillar
You will be thrust into the middle of a battle around the Sector 7 pillar. Shinra is in the process of trying to bring it down to destroy the AVALANCHE hideout in 7th Heaven. The orange guy on the left is selling consumables if you need any refills. Start trekking up the stairway to the top. If you gave Aeris any important Materia make sure you put it back on Cloud or Tifa. Any enemies encountered along the way are easy and no complicated measures need to be taken to bring any of them down.
When you get to the top you’ll see Barrett firing into the sky like a mad man. Talk to him to get the story rolling again. When given the chance make sure you load all three team members up with appropriate Materia and top of the line weapons/armor. The opportunity is given because a boss fight is coming up.