Yo dawg I heard you like upgrades

Upgrading a turret is a great way to get the most bang for your buck. The more upgrades you have installed on a single turret, the more expensive they become, so choose wisely.

Buying the option to set a target mode gives you more control over a turrets behaviour. Should it focus on the enemy closest to the base, on the one with the highest or lowest health? Should it take down particularly fast or powerful bad guys first?