Tower fires missiles from the tower after a period of time. Missile damage is determined by Smart Missiles damage. When Smart Missiles are not unlocked, they will do the base damage of 14x. When the lab is unlocked in milestones, the display will show that missiles are fired every 20 seconds.
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Spotlight will not fire missiles until the first level is unlocked and frequency is 19 seconds.
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https://the-tower-idle-tower-defense.fandom.com/wiki/Lab/Spotlight_Missiles#Spotlight_Missiles