Defend the path in multiple locations, upgrading your units. Choose from a number of different units and build their levels across many skill trees. Along with one-off levels there are storyline quests to follow.
The game engine has been revamped for this entry in the Protector series. Unit upgrades are displayed with a small skill tree. You can hire heroes, each of whom brings a different selection of units for you to use. This replaces the direct unlocking of units in the previous games. Your character in the game has attributes which can be levelled-up, and at the start of the game you select personality traits which will make the other heroes more or less inclined to join you.