Next, we head right, to Junk Man's stage. Head right until you see a platform suspended in the air. Defeat the enemy on it, and then the enemy on the next platform, to reach the bolt on top of it. Just to the right is a pile of junk. This is a Gockroach S nest, which releases a steady stream of Gockroaches until it's destroyed. Gockroaches are a little annoying because regular shots fly right over them. Take them out with charged shots. Take out the nest and head right, down the ladder.
The next area just has a Gockroach and a nest. Take them out and move to the following area, which is an elevator. You'll have to fight the flying Metalls, which fire shots diagonally down left and right. Thunder Bolt can sometimes take out several of them at once. Fight them until the elevator stops, then proceed through the door.
Watch out for the lava (or maybe molten metal) in this area. It will kill you. You can freeze it with the Freeze Cracker, though. Remember that you can fire that weapon diagonally. In fact, there's a secret path here if you have the Freeze Cracker. Scroll down for details about the alternate path, but you'll have to visit this stage twice, anyway, to get everything.
If you don't have the Freeze Cracker, or just want to go for the Rush Jet
To go for the Rush Jet, head right, dealing with the Gockroaches on the way. Destroy the nest, head to the next area, and destroy the next nest before heading up the ladder.
The Thunder Bolt is handy here. Fire it at the generator on the floor to start the platforms moving. Now you can use them to easily hop between ladders. You might be tempted to ride them up, but you can get crushed against the ceiling if you do this. There is a health item in the upper right.
When you climb to another floor, use Rush Coil to reach the ladder on the upper left. This will get you the Rush Jet, which will let you fly using Rush for a limited time. Useful! Climb the right ladder, then avoid being crushed by the elevators as you make your way to the left ladder.
There's an enemy swimming in the garbage here. You can destroy it by damaging its head enough. Shoot the generator with a Thunder Bolt to start the electromagnets. The magnets will carry you over the pit, but they'll also suck up debris which you should destroy without touching. The enemy in the junk will harass you if you spend too much time down low, so just make your way to the right and slide into the next area.
If you have the Freeze Cracker and want to go for the letter S
Freeze the magmafall in the area with the lava. It will crumble away, revealing a path with a ladder. Climb down and freeze the magmafall to the left to reach the S. From here, jump over or freeze the small magma pools. Freeze the large one for sure and walk across, avoiding the falling debris. Climb up the ladder, and either grab the 1up or just continue through the door.
Here's another elevator like the last one. Take out the enemy and head up the ladder, then take out the Bunby Tank and head up the next ladder.
This is where the two paths converge.
The floating platforms here won't move if debris from the machines above lands on them. They'll just stop and start shooting. Destroy anything that lands on them to clear your ride. Take it slow. There's weapon energy on the platform above the ladder to the next area.
It's safer to destroy these turret enemies as you come across them. To the right is the door to the boss, so make your way there.
Here's Junk Man, weak to Thunder Bolt. He'll cause junk to drop from the ceiling, so avoid it. He can draw debris onto his arm to create a large block, which he'll throw at you. It stays in the corner of the room after he throws it. He can tunnel into the ceiling and come down on top of the block to destroy it, or damage you if he hits you. When he destroys the block, the debris will form a shield around him. He can throw the shield at you to trap you in place for a little while. He'll follow up by hopping into you. As you'll see, each of his attacks leads into the next attack. He can hop into the air and toss a piece of junk at you, so slide when he jumps high. His pattern is actually pretty easy to predict this way.
The Thunder Bolt does heavy damage, stunning him and interrupting his attacks. He will follow every hit from Thunder Bolt by hopping all the way across the room and throwing a single chunk of junk while he's in the air. Use this to keep him doing this one easily-avoidable attack over and over until he's dead.
Defeating him will earn you the Junk Shield, a very useful weapon that surrounds Mega Man with a barrier made of junk, which absorbs shots and defeats weak enemies.
NEXT: Freeze Man