To accomplish those you can work them together by getting the opponent down to -50 you have the best chance of getting a 500 kill shot. Now a days with the new heavy weapons is much easier than when I did it long ago.
I think it was against GOD mode map when they use to have it.
Be nice if they reset them all so we can re do them
Maybe add some new ones like instead of just a drone only kill make it a drone EXP only and a drone ELE only maybe even a mele stomp only etc