Thunderstorm Skull

Thunderstorm Skull Effect: Each enemy gets a “rank promotion,” making them stronger

Thunderstorm Skull Location:

The “Thunderstorm Skull” can be found on the level, “The Covenant”, after you take command of one of the Hornet vehicles. Fly towards the second force field generator (the one the Arbiter disabled), and land. The skull is waiting at the very top, at the end of the ramp extending over the sea.