Skull Effect:Each enemy receives a field promotion and is upgraded to their next available level.
Campaign Scoring Multiplier: 1.5x
Skull Location:The Thunderstorm Skull is located near the middle of the seventh level, The Covenant.
The Skull is located in the part of the level after you take command of one of the Hornets. Fly towards the second force field generator (the one the Arbiter disabled), and land. The skull is located at the very end of the ramp that extends out over the sea.