Cycle of life and death

Defend your cyrstals of life, which eminate light into the great void!
The hordes of hell attempt to destroy and eliminate.

Controls:

WASD :    Move around
Space :     Move up
LeftShift:  Move down

Left Click: Spawn a stationary minion to defend against attackers, sacrificing themselves for the greater good.
Right Click: Spawn a walling crystal, which will stop any attackers but can only take so many hits.