Spend coins to improve survivability and add support units. Changes apply the next time you start a level.
Drone: auto-tazes foot enemies only.
Humanoid Robot: uses both (gun vs vehicles, tazer vs foot).
Coins are earned at the end of each level based on score + a clear bonus. This shop is designed so early upgrades are cheap, but maxing everything takes time.
You earn coins at the end of each level based on your score (and some bonus for clearing). This is a simple economy we can rebalance later.