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Thunderstorm is a gold skull appearing in Halo 2, Halo 3, Halo 3: ODST, Halo: Reach, Halo 4, Halo: Spartan Assault and Halo 2: Anniversary. When activated, it elevates the rank of the enemies (and in some cases allies) that spawn throughout the level.
In the large room after the armory, you need to use a Crouch Jump to get onto a light fixture on the right wall (right of the room when you enter) and then jump from there onto the higher area. There is a series of diagonal beams. Walk up one near to the end of it and use it to Crouch Jump onto one of the rails. You can fall between the rails, so be careful. Once on the rail, walk down it until you can jump onto the highest platform. Then melee the trashcan away from the wall a few times, the Skull is right behind it.
It is also possible to Grenade Jump up to the platform if you can't stay on the rails. The Sputnik Skull helps a lot here, but it's possible without it. Just get on the ground near the platform the Skull is on and Grenade Jump. You also don't need to melee the trashcan out of the way, but it will reveal an interesting hidden object. Near the Skull is a burning cigar that looks like a Sweet William Cigar, the type that Sergeant Johnson is seen using.
- When you hop into a Hornet to fly to the third tower, the title If You Want It Done Right should be displayed. If it doesn't, then no skull will appear.
- On your way to the third tower, you will see the second tower which was disabled by the Elites. Fly over to it.
- There is a long, flat, semi-enclosed part of the tower that extends out over the ocean. There is a very tall ramp that leads up to it. At the end of the extension you will find the Thunderstorm Skull.
When activated, Thunderstorm increases the rank of any enemies to the highest rank possible that appear in each level. For example, Brute Minors that would appear in the levels they are featured at would turn into Brute Ultras. Not all enemies are affected; for example Brute Chieftains will not turn into Brute War Chieftains even though the War Chieftain is a stronger version of the regular Chieftain. As a result of these promotions, enemies will fight smarter and be more durable.
- In Halo: Spartan Assault, using this skull along with the Black Eye skull and achieving the gold point threshold will unlock the 'GASO' star.
- However, this star can only be seen on Halo Waypoint.