If It Moves... (EVA-8 Shotgun)

is one of the many challenges in Titanfall.

How to Get
The easiest way to do this challenge is to just unleash into groups of Spectres, Grunts, and Marvins. There's no real special way to do this other than sticking to it and trying to rack up the kills.

The last level of the campaign is a Specter factory. If you allow the enemy to hold A, a lot of Specters will spawn. Camp that base, kill Specters, and don't take the Hardpoint to get through any Specter or generic kill challenge quickly.