Your only weapon to defend against enemy invasion being stuck inside a canyon is your gravitational cannon. Shoot enemy units up to stop them from entering your territory. Good luck!
Fire gravitational projectiles into enemy units.
Make sure you don't let too many units through and don't allow your canon to be destroyed.
Use the mouse to fire the canon. Click the centre and drag it back to set the direction and power.
The more power you give to a shot, the more unstable it will be. Instability will add a chance of the mortar exploding before it is fired, causing damage to the canon.
Enemy units will bounce back or explode when they are hit.
Having them bounce against other units will do further damage.
You will receive skill points as you level up. Use these to upgrade your gun, or invest in special abilities.