Tower Mods are a mixture of Terran and Alien technology that Sparks has developed to boost different stats such as Range, Damage, and Turn Speed on our Towers. There are 3 standard tiers for each stat: Iron, Bronze, and Silver that offer better percentage increases for that stat.
You can also earn a special Gold Mod that will give certain Towers a special ability such as additional infantry units or reduced prices to build.
You earn Mods through Events rewards and you can only get Gold Mods through completion of the entire event.
Once you have earned a Tower Mod you can equip them through the Loadout Menu as you are starting a mission. You can only equip one type of Mod at a time and you can’t stack Mods to gain higher stats. For example, once you have equipped a Damage Mod for a Machine Gun Tower you can’t then equip a Damage Mod to your Laser Tower.