Cannot be attacked.
Remove the destiny cards of your colour from the destiny deck. If you lose your alien power, shuffle them back in (remove them again if you regain your power).
You have the power of invisibility.
Players may not attack your foreign colonies if they draw their own colour from the destiny deck.
Instead of drawing a destiny card you may elect to attack Unseen on any of their home planets or on a foreign colony in your system. If Unseen is not in the game, replace this card immediately with a random flare from the unused flare deck.
Play when an opponent draws a wild or special destiny card. If they draw wild destiny, they may not attack you. If they draw a special destiny, you are immune from consideration.
While it's nice to have your foreign colonies more or less secure, the biggest advantage is the conservation of resources - ships and cards - that would otherwise be lost or spent on the defense. Unseen will still lose ships as an ally, on the offense, and to cards and powers like Plague, Hate, Vacuum, etc. In this way, Unseen is weaker than Zombie.
Not being attacked at home is good, but better than it sounds. The main advantage of holding home colonies is preservation of your alien power, but retaining your power is only usefull if your power does other things besides retain itself.
One advantage Unseen has is that the other colours will be drawn more frequently, meaning the other players will be apt to lose their powers sooner. Essentially, Unseen encourages infighting amongst its opponents.
Unseen hoses Shadow and partially hoses Dictator (Dictator still choses whom is attacked by Unseen). Will mostly hoses Unseen but still cannot attack Unseen in Will's own system.
Unseen cannot be zapped except when playing its super flare.
I'd like to hear feedback on this - particularly if it's too similar to an existing classic or homemade alien.