Darius Gaiden/Z'

Great Thing
Great Thing is a mechanical sperm whale, and it has three attack phases, all of which are deadly, especially if you are ill equipped.

After it's approach, it will deploy a few subvessels that occasionally attack forward, and will cycle through the turrets attached to the main body:

After firing a shot at the ground, Great Thing may change it's attack when if it took enough damage. When it does, it will begin with launching drill-shaped missiles. In addition, it may start production of rotating cubes on higher difficulties.

When critical, it will proceed with its final pattern. While experienced players can defeat it before it shoots lightning, this requires you to collect and retain powerups to the maximum level.

When it is defeated, you will receive any end-game bonuses, and get to watch the ending.