The fourth stage is a vertically scrolling level that takes place along a waterfall. As the view of the screen continues to climb with you, it is possible to die if you fall through the bottom of the screen, even if there used to be a ledge where you fell. As soon as you begin, two soldiers appear right above you. As you jump up to meet them, they will light the bridge on fire. However, the only harmful part of this blaze is the large flame that moves back and forth. If you do not possess any special weapons when you reach this bridge, two capsules will appear. The left one contains a Barrier, and the right one contains the Rapid fire upgrade. If you do manage to capture the Barrier item, the best strategy is to race up to the top of the waterfall as quickly as possible so that you continue to benefit from the Barriers invulnerability while you attack the boss. Otherwise, proceed carefully.
Scuba diving soldiers lurk in certain sections of the waterfall itself. They launch cluster bombs up into the higher levels of the falls when you are with range of their weapons. The bombs explode and fracture into three parts. Stay to the side when you see these bombs rising to meet you. Don't bother trying to shoot the scuba soldiers, simply advance high enough up the screen to remove them from view. As you continue your climb, there are several chutes which release falling rocks. There are also several places where floating footholds hover left and right across wide gaps between platforms. Be sure to stand clear of the chutes which release the rocks while you wait for a foothold to come closer. A weapon sensor near the top can provide you with a Spread gun. The weapon is likely to land on the nearby foothold.
A large statue situated over the entrance to the second base is what you'll find at the top of the waterfall. It packs a lot of firepower that is backed up by pairs of soldiers that run in from either side of the screen throughout the entire battle. There is a 5-way turret situated in the center of the statue, flanked by two rotary cannons. The turret only fires once every once in a while, but the turrets are in constant operation, so they should be your first target. All the while, you must watch out for soldiers that run on to the screen. When both turrets are destroyed, find a safe place to stand just to the right or left of the very center, and fire up at the turret until it is destroyed. With that gone, you can freely fire upward at the sensor located in the head of the statue. When it is destroyed, the gate to the second base will explode, and you will be able to jump inside.
The fifth stage is the second instance of a 3D maze through the interior passages of an enemy base. This one is slightly longer than the first, and you are given a time limit of one minute and 50 seconds. Quite often, each room will feature two or more defensive wall turrets. In addition, these turrets, along with the power seals, may not necessarily be placed at a height that you can easily attack from standing. You may need to jump high before firing your gun in order to hit the seal. In cases where it may take more time to destroy the seal than usual, it may be safer to destroy the wall turret first, unless you are confident that you can destroy the seal without getting shot.
Once again, a map is displayed at the top of the screen to help you navigate your way through the base. To reach the core, you must choose the following directions: left → right → left → right → right. Once again, the last power seal that you encounter will be larger and take more damage than the rest. It is also located behind a defensive barrier which you must first destroy. Be aware that while you are shooting the wall, it is quite possibly for an enemy soldier to toss a grenade at you from the other side. When you destroy the final seal, you will reach the boss of the base. If you don't have any special weapons to assist you, you may find the next battle quite difficult.
The sixth stage, like the third stage, is a fixed 3D screen. There are four sensors again, and just one turret, but they are arranged across three levels instead of two, with the turret at the very top. In addition, enemies will appear from the left and right sides of the background. White enemies run across and leap down to attack you while red enemies reach a point and stop to shoot down at you. The red enemies have a fairly fast rate of fire, so it's not a good idea to let them linger. Once again, the boss will not appear until all four sensors have been destroyed, so it's important to remove the turret at the very top before you go after the last sensor.
Once the sensors have been destroyed, the boss of the stage appears at the top. This boss contains two entities, both of which must be destroyed in order to advance to the next stage. Instead of traveling left and right like the boss of the first base, each instance of this boss splits up and phantom images go in both directions. It is only vulnerable to attack when the phantom images come back together. All the while, each boss will release a small bomb that first drops slowly to the floor until it homes in on your position and rapidly picks up speed. These bombs are small, but they can be shot down before they reach you. It's best to destroy them before they move too quickly. They have a tendency to veer to the left, so you are a bit safe on the right, but not always. Try to focus your fire on only one boss until it is destroyed before moving on to the other. Once both instances of the boss are destroyed, you will advance to the next stage.