Joe starts off outside a Neo Zeed base, with the forest behind him on fire. Lots of Neo Zeed soldiers are around, including standard machine gun totting troops, gun emplacements, grenade launchers and boomerang throwers. Watch out for the land mines dotted across the floor at various points as these will explode about half a second after you step on them if you aren't careful. You'll also have to leap over canisters which will blow their tops when stepped on.
Before you can reach the bases entrance there is a small squad of grenade launchers who need to be dealt with, I'd advise moving slowly and taking them out one by one to get by without taking a hit. Now, remember how in the previous level's mid-boss there was another robot who flew off? Well, here he is again.
Thankfully this robot is a bit dim and his main strategy is to try and knock Joe down by ramming into him. Whilst he's quite speedy double jumping is an easy way to avoid this attack. His only other offensive method is to blast of laser shots, which can be blocked meaning this attack is also fairly useless. Keep hitting him with shurikens for a quick victory.
Now inside the factory, the place is swarming with soldiers and there seem to be an awful lot of robot godzillas in the background, although none of them have been activated yet. The main thing to remember here is that you must destroy the floors with the bomb items to progress though this part of the level. It starts off easy enough but later on you'll soon have to do this without falling to your death.
It's fairly easy to navigate through the factory, but a little bit in you'll find that some bombs have been put there just to destroy a floor which you don't want to be destroyed, so be careful when killing enemies who are near to them.
This factory is large and requires a lot of jumping around to progress, although really it's nothing that challenging. However, once you reach the point in the middle screenshot above, you can either use the wimpy way (which I always use) of using the mijin magic to blow yourself up and break open the bomb item on the other side of the wall to destroy the floor beneath you and let you go on at the cost of a life, or there's the harder route of getting all the way to the bomb to blow it up without using any ninja magic. Your choice. The next section involves more floor destruction to make your way up to the top.
Getting to the top of the factory is quite a trek and involves a lot of climbing up pipes and leaping off walls, as well as trying to avoid being shot. You'll also have to use a few moving platforms and let them take you up to progress through certain parts. When you finally do reach the top floor, head to the right and toward the door to move on.
The next room is pitch black, until a pair of red eyes appear and the ground starts shaking. A massive robot godzilla-type monster appears and the room lights up, beginning the most challenging boss of the game thus far. Robozilla will move around and try to get near you, and whenever it takes a step a whole load of garbage will fall from the top of the screen so be ready to move. It can also shoot green fireballs at you in three shot bursts, although you can block these.
The other attack this boss has is a fire breath blast which can do major damage to you so try to avoid being hit by it. You can always tell when it will use this attack as it roars just before unleashing it. The only weak point this boss has is it's head, so keep firing away at it until it explodes. You'll then have to destroy what appears to be the robot's brain unit, and the only way it can attack you is with barrages of the green fireball shots. Thankfully these can be blocked so just alternate between blocking and throwing shurikens.