Principle: power down completely, and destroy the middle boss quickly when it appear, the Intermediate boss cannot be destroyed quickly so choose the left and right side boss, and then there will be endless UFOs, the game is also freeze in this stage.
Don't shoot the red UFO or just don't leave over 1 power up in the screen, if there are two more power up in the screen, UFO will not appear any more.
This bug is found by my friend, you can use it for counterstop but spending a lot of time
