Round 4 takes place in a junkyard. There are no new enemies here, but they are plenty of soldiers, especially the ones who have guns and grenades. Try and make good use of the garbage, as it can often protect your from enemy fire.
The amount of soldiers in this section means it can be hard to avoid their bullets, so be ready to use a shuriken spray to take down everything quickly. Like in the previous round, a single flamethrower soldier guards the end of this section.
The next section is set in a factory. There are a lot of hazards in this section, the first one you'll come across is a conveyer belt. These conveyer belts often move in the opposite way you'll want to go, and also often lead you into more traps. The most dangerous hazard in this section is the molten lava, which will kill you in one hit if you fall into it. Yet another hazard are the crushers, which thankfully won't instant kill, but still hurt.
You'll need to move to the right of this stage, then up, then to the left, then up, and then move to the right again. The only enemies to worry about here are the soldiers, but their shots can make you fall great distances if they hit. Towards the end of the section there are several flamethrowers built into the walls, watch out for them. Right at the end of this section you will have to use a piece of falling junk to move down. Move off it and to the right to head down a small corridor and end this part of the round.
The boss of this round is the Master Attacker. He is so strong he can pick up wrecked cars and throw them at you. At the far left and right of the screen are some platforms you can stand on to help avoid his attacks. When he throws an object, just jump or somersault jump. His only other method of attacking is a dashing charge, but it is easy to tell when he's going to use this as he'll pause for a second before dashing.
His only weak point is his head -you can hit it when he's busy picking up an object. A more wasteful method of hitting him is to keep shuriken spraying him, but this will use up a lot of shuriken very quickly. As you keep hitting him, his skin will turn greener and greener, and when he dies, you'll find out why he was so powerful -he was a robot all along!