I was the VFX Lead for the Forerunner Campaign Missions on Halo 5. I set up and designed the environment effects and texture sets for the sky energy, lens flares, fog atmospherics, radial blur, and screen effects.
The funny thing is that the energy effects in the sky happened by accident... It was actually another effect I had for something else in the level, but one day we had a game engine bug that flipped our rotation coordinates and scaled things up by 10x. This showed up as a result and the art team liked it. Pretty crazy! This didn't ship in the final version of the game, but it was something I thought was cool to show.
The distant cloud skybox and lightning effects were done by another artist.