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There is a Node called ScreenPosition in the Material Shader in UE4 which basically pans the texture you are using everytime u move. I think they just used the Node for it, it's simple but has an awesome look to it.
Very close guess! We are actually using the Absolute World Position node to grab the position of the gun in the world. Then we mask out the Z axis so we can use the X and Y to offset the texture in their own axis.
If you walk in a straight line on the X-Axis of the world, the orb will spin horizontally, and if you walk on the Y-Axis, it will spin vertically! You would also notice that if you go straight up or down, the orb won't move ;)
Similar to what we did on Spectrum for the color shift, but in this case we used all 3 Axis of the Object Position Node to control everything.