PewPewPew! Light towers spew out a wall of bullets. Although they're not the most powerful, they more than up for it in rate of fire! Sweep the skies to keep the enemy at bay.
Heavy towers (yellow):
Heavy towers can pack a real punch! Their rate of fire may be much slower than light towers, but they make up for this in being able to damage groups of enemies with their splash damage radius.
Laser towers (purple):
Laser towers are slow, expensive, and affect your carbon emissions... but they will cut a path through the enemy like soggy tofu. Beware, they're highly vulnerable in-between shots so make sure you keep these towers covered by your other defenses.
City (green):
Cities generate defensive shields in a hemisphere around them, protecting themselves and any other tower within range. Upgraded cities can protect against more hits, and regenerate their shields faster over time.
Watch out! Enemies approaching from the side are likely to reduce your shields!
Overdrive:
Once charged, the awesome destructive power of the Overdrive device will clear the screen of enemies. Charge it by destroying enemies and pushing the charge meter up to 100% (or purchasing it in architect mode!)
City in architect mode:
In architect mode, the main goal is to protect the cities - it's game over if all are destroyed! Thankfully, they also help in generating resources to build more defences - The more cities you have, the more you'll get!