So with the big improvements to ground combat, I thought that it would be nice to have an enemy that fully exploits these new new mechanics. This Spoiler would have a chance of spawning on habitable and near habitable terrestrial worlds/moons. They start out as a colony with of ground force production centers, enough population to service those centers, and a massive number of ground forces. They would have the unique feature of being protected by a planetary shield, which are projected by buildings that the player can study after they are defeated. The planetary shield absorbs damage from weapons fire much like a normal shield, but with far greater recharge rate and strength. Ground forces and fighters, however, can still be deployed onto the planet.
The big thing with the Crusaders is that they want to fight, and fight honorably. They consider space combat to be deeply dishonorable, so they will not participate unless forced to. Their ground based anti-ship batteries will not fire on nearby ships unless fired upon first. They will have a timer that is reset whenever an empire fights them on the ground, so long as said combat lasts for a little while. When that timer hits zero several massive troop transports, which are armed with weapons and defenses scary enough to make Invaders wary, will move to the nearest large population and drop off their troops. If the planet is taken it becomes another Crusader world, where the population will be drafted into their armies and shields erected. The troop transports will not use their weaponry unless attacked by a onworld weapons batteries or space based enemies. The message mechanic can be used here to make sure you know not to shoot, as one of their ships can message either your planet or a ship.