The fourth stage is a vertically scrolling section.
 Part 1
The stage boss looks like a small crab-like creature. It's main threat is a spread of bullets that are somewhat packed, as well as a vertical charge upward. However, it is not too difficult to defeat.
 Part 2
Here, the enemies begin to pick up. The main threat are the blobs attached to the sides of the wall, which approach when they are level, and turn diagonally when they are close. However, you can disarm most of them as they appear by holding at the top of the screen: this exploits a detection bug which wraps around the top of the screen with the bottom, causing blobs (and other enemies) to trigger as soon as they enter. You won't be able to do this to the first two blobs, but as long as you hug the top of the screen, they can't hit you.
First, watch the center for a speed powerup, followed by a protect powerup. There is also an orb powerup that appears when the left-hand jut approaches.
Eventually, the background will stop, leaving only a black area. Watch your fire here, there's two balls that are launched upward, which will break apart if hit. If you shoot one, make a slight dodge to the left or right. After the second ball is a missile powerup.
This leads to the stage boss, who occupies a large vertical column. You may travel on the left if you want quicker access to the target's weak point, or on the right if you value safety.
The weak point of the boss is a single eye. While it does shoot a laser, it's possible to position yourself so that you don't get hit. In addition, hitting the boss also cancels the laser, allowing you to constantly shoot the eye until it is popped.