2 0 0Alien Ruler DLC *** Spoiler - click to reveal ***After you kill the Serpent Ruler you can complete research to make a Serpent Suit Armor. The earliest you can complete this achievement is when you have made the armor and equipped it and encounter the Berserker Queen. When you encounter the berserker queen you can use the frostbite ability on it and the achievement should pop. Or you could wait until the Archon King and use either the Frostbite Ability from the serpent suit or the Rage Strike ability from the R.A.G.E. suit on it. If you kill either of those 2 rulers without using a suit ability on them then you cannot get this achievement in that playthrough.