King Kong 2: Ikari no Megaton Punch/World 4

The fourth world is broken up into a couple of sections; a southern section, a middle section, and an eastern section. You begin in the southern section, where you can collect a Speed Potion, and find the Konami Logo which summons Konamiman to heal any damage you have sustained.

In the middle section, more items are found along the top row of screens. You will have to be a little more diligent in order to find the various doors and items hidden on some of the screens, as they may be hidden below the red circles. You can typically access any of these circles that are positioned south of the traversable paths. While you're there, look for the Rock Case, a Hyper Bomb, and another Speed Potion.

Once you reach the eastern section, head south first in order to collect the Artificial Heart that is hidden in the lowest screen. Then return to the top in order to reach the hideout of this world's boss. Don't miss the invincibility granting Star Rock one screen earlier.

Boss
The boss of World 4 is a mass of cells that is surrounded by four smaller masses that serve as shields. The smaller masses rotate around the center mass, and fire bullets throughout the room. Rocks are a good strategy to use against this boss, but it is far more effective to throw them up or down as opposed to left or right. Throwing them laterally increases the likelihood that the rocks will be blocked by the smaller masses.

Once the boss is defeated, you'll want to return to the southern section of this world, and access the warp zone closest to the starting location of the world in order to advance to World 6.