Battalion Defense

Well this is pretty much a tower defense, however unlike any other tower defense I am aware of, nearly all of the towers possess the ability to improve themselves by doing nothing other than being active. There are three different types of towers.

Towers:
Just your run of the mill towers, you build them, they attack, they have no ability to improve themselves, and they require no food.
Units:
Each unit can level up, up to four levels, by killing runners, attacking them, or using abilities. As they level up, they will gain a bonus to their attack, and additional abilities unique to their unit type. Each unit also costs one food, but receive bonuses from their leaders.
Battalion Leaders:
Battalion leaders will prove to be the most useful tower types. Each can level up to level 10, through the same methods as units, however they possess the power of leadership. Each leader will be granted a radius of units to manage, those units will be granted bonuses according to their leading unit. As their natural abilities can, battalion leaders will improve their leadership as their units gain experience.

Note: Only battalion leaders will be heroes, and will use triggers to gain experience and so experience will only be gained through one's own actions.