Visaks

The Visaks are an invasive predator that attacked all main species- Humans, Tolana, Soli, Rhonaians, and several other minor species. They initially attacked on massive scales, decimating cities. 
They are about 7 feet tall, with human-like builds, bulky muscles. They wear thick grey armor, which is insanely durable and repellent to bullets and weapons. Their faces covered in the same armor too, oval-shaped heads with red eyes, Their mouths are large, making a large O-shape when screaming. They have shark-like teeth, small and sharp incisors that cut through most flesh easily. When they are about to die or injured, they dissolve into thin air, allowing for no study, research, or examination of the bodies. 
Initially, the Alliance thought it was a heard of invaders, nameless and faceless enemies bent on destroying as much as possible. The Visaks did not try to communicate, nor demand surrender terms. They just wanted to destroy as much as possible. They took out New York City, London, Tokyo, and Shanghai. They took out major cities for the Solis, Tolana, and Rhonains. This caused the Alliance to form, as for the first time, they all had a desperate need to take out a common enemy. 
Within each species, they recruit one candidate to represent them with the goal of creating a special opps unit, a specialized team that can research and experiment with new tech that can later be applied on a larger scale. When the Visaks attack Daku with a small unit, it baffles the alliance but presents itself as the first opportunity for the special opps unit to attack. They clear out the outpost, in the process learning that there's a whole additional element to Visaks: Mind control. The Visaks had manipulated the outpost leaders into purposely sabotaging the planet. This revelation is disconcerting on multiple levels: it shows something of concern for further Visak attacks, as well as intentional strategy and manipulation as opposed to massive destruction. 
When the unit attacks a viask base, Lee discovers a Video clip showing a lab with Visaks in tanks, being cloned/created. He sees a human arm with a bent finger that looks all too familiar, an intelligence officer from Mars. He has a breakdown, realizing humans, possibly his people, are behind it. But he has strict order to deliver the tape to his people. He struggles with his choice. 
When the Unit launches the final mission on the Visak cloning area, Rainey is captured and cloned. The real enemies are another alliance of all the species, in formation for over a hundred years, bent on destorying all political and economic structures to start over.