These strange body-less creatures coming from no where to invade your world. Your world is filled with Light and they want to turn it to darkness. You goal is to defend the portal and drive the intruders away. The only thing protecting you and the portal is the magic barrier but the enemies are weakening it gradually. The enemy fears the light so that's what you are going to use. Chop trees to make torches. Use them to scare and hurt the creatures. Place them near the barrier to keep the creatures away So that the barrier can repair itself and expand. If you expand it enough the light will be too much for them and your enemies will be forced to leave.