Go to winter's run. You need to run through it and get Draxsis down to 1 shot with three of coins active. Make sure you don't activate it until you have to kill him because his guards are magors/ultras. You then need to kill him with a rocket launcher with your guardian close enough to be killed by the blast. He should drop an engram which you can pick up when you respond, even though to beat the mission you will have to kill him again.:)