HONESTLY, just an idea!
Keeper: ranger with three barrels, stacked in streamliner fashion. very evasive. Crusher: green annihilator who fires massive bullets that explode into normal bullets... that explode into gunner bullets. executioner: red spike thing that dashes into targets, dodges bullets (sometimes) and has low hp. watcher: manager with a pair of auto turrets. fires drones, and every once in a while, factory tanks.