So I've beaten the game with every victory, and I have reached the following conclusion. Aliens are meant to be killed. Scavenging, 2nd tier of might, is easily the best reason for aliens in the game. Slaughter in the name of science is amazing. Even if you go harmony, when you build the world seed, all the aliens will go hostile towards you. I played my harmony victory leaving a bunch of aliens free to roam my territory. When I built the build, they all attacked it. I wiped them out and realized there is no purpose to aliens other than to annoy you and give you science by scavenging. In previous civ games killing the barbarians for culture farming was a thing. Now its killing aliens for science. The next to culture virtues, Adaptive sciences and Martial meditations are also very good, so you don't really lose anything going into might so heavily. Specific Aliens The Kraken is a very slow moving unit that will one hit most boats and units. It moves 1 unit. If your boat fires 2 spaces, it will take reinforcements to box you in to kill your unit. modification from ultrasonic fence does prevent destruction of trade units by this unit. The siege worm. Early ranged units do almost no damage to it, lure it near of of your cities by feeding it a weak unit, then it will stay in range for city bombardment to actually hurt it. It tends to move away when its almost dead so finish it off with something. Loves to spawn from dark tiles just outside your boundary. Ultrasonic fence does keep it out. The modification to trade units also prevents destruction. Everything is basically equal to a level 1 marine, they get pwned by anything higher. Level 3 plus can solo swarms of aliens. Whenever you receive an alien unit from an explorer find, it has decent movement, heals in miasma, and I basically use it to harass the enemy cities early as it moves and heals well. The flying one in particular is weak but moves very well. All aliens hate your tamed alien... so expect lots of aggression on your new pet. The harmony special units kind of suck, the ones that utilize alien creatures... they seem to be very fragile in my limited experience. Any thoughts or questions welcome.