After some dialogue, he attacks you with his ship. He uses mainly a shooting attack which he shoots from 2 places (in front of the ship and behind it) which deals 15-20 damage; you should keep your shield up. Then he calls a Nnengral to support him. Killing it gives you a grenade, which is important to defeating the boss. It will eventually create a vacuum beam below it, which will drag Arkus in and deal heavy damage if he is hit. The solution for this is to throw a grenade towards the beam and keep back. The grenade will be pulled towards the ship and will explode, leaving the boss vulnerable to Arkus' attacks. After awhile, the ship will recover, and its attack phases will reset.