After you make it through another part of the alien spaceship, you finally reach the main engine.

How to Destroy the Main Engine

To damage the main engine, you have to wait for the spinning golden rods to open up. When they are open, wait for the northernmost tile in front of the engine to close. (If you fall in the opening, you go back to the underground room with a capsule, laser gun, lightning gun and magic potion.) Jump onto the closed northern tile and shoot the engine as many times as you can. (If you stand south of the tiles, you'll get hit by spiked balls from the holes in the south corners.) The southern tile opens earlier than the northern one, so you can use it to warn you to jump off before the northern tile opens. If you take too long to deal damage, the engine will start to recover its health. If you can damage it quickly enough, you will eventually destroy it.

Moving On

From the engine room, go west. Pick up the four hearts and the laser gun, and then you can kill the falling monsters until your health is full. These monsters will move southward, but if you go one square to the left of their path, they will just jump side to side without hitting you.

When you have refilled your health by killing the falling monsters, go north until you reach the room of Zoda's True Form.