Death Reincarnate (Mobility Kills)

is one of the many challenges in Titanfall.

How to Get
The easiest weapon to use this with is either the grenades or the various sniper rifles. Just get used to missing the shot, because this one does take quite a while to do.

Though the tip above works, I've been using this tactic: Wait to get rodeoed, eject, and then kill the enemy pilot in the air. When you manually eject with someone on your back they will fly up with you and be right in front of you. (Just be ready). Cons: Losing your titan. Pros: Easy challenge kills.

Another way to get this challenge is by using the Stryder titan with Nuclear Ejection, Survivor and Minion Detecter. Once your titan gets doomed use the survivor time to look for a group of grunts/specters. Once in position eject and get 2-3 easy kills.