This is a 3d, single-player, strategic tower-defense game made in U3D.

The Story:

The whole Earth is in danger now because there are alien invaders. If the energy storage, which is various crystals, is destroyed by them, not only the human beings, but also all the living things will be soon extinct. However, you have the control of the gravity ball to protect our homeland. Please save us as quickly as possible.

Basic Skills You Need:

Dragging the gravity ball: