As the overly confident Harbinger flew away because he wasn't being paid enough to spend longer than 2 minutes in the game, Marauder made his final approach towards the bloodied Shepard. Everything had transpired according to his plans. Marauder got close to Harbinger to get close to Shepard, not to kill "yumanity's" first Spectre but to save his/her gender inspecific ass. He was going to warn Shepard to avoid any more films like The Happening... and secondarily to stay away from the controversial ending that awaited him on the Citadel.

Marauder Shields's ultimate sacrifice was about to pay off. He had let himself become huskified, kneeled as the servant of Harbinger, and abandoned two of his progeny in a nursery sandpit in order to reach this moment.

Marauder Shields.
Son, lover, and father was about to fulfill his destiny, entering the annals of galactic and BSN history as the savio-

But then Shepard shot him in the head.