Halo 2
41 Achievements
1,000
King of the Scarab
Acquire the Scarab gun on the Metropolis level, any difficulty
20
How to unlock the King of the Scarab achievement in Halo 2 - Definitive Guide
The Scarab gun is an easter egg on the Metropolis level. It looks like a Plasma Rifle but it shoots the same kind of energy shots that the Scarab does (the giant four-legged tank that is ravaging the city in the Outskirts and Metropolis levels).
Getting to the Scarab Gun is kind of tricky, as you need a banshee to get to it, and the area where it is doesn't have any banshees available.
Right when you start out kill all your teammates and head over the bridge. If you don't kill your temmates they will destroy the Banshee that you need. Kill all then enemies on the way over. When you get to the other side of the bridge two Banshees should appear. Shoot at one to get it's attention and get it to follow you down into the tunnel.
When the warthog shows up destroy it as well. Keep moving through the tunnel all the while making sure that the Banshee is following you. If it turns around and heads back shoot at it to get it to follow you. Once you get the Banshee past the second roadblock lure it into the smaller tunnel.
If the Banshee gets stuck, shoot off its wings (don't melee, shoot). Take it down the side tunnel to the left. As soon as it's says "Loading.... Done", board the Banshee (if you don't it will dissappear). Fly out and up, up high in the sky there are two bridges between two skyscrapers. Fly to the middle of the one closest to you and you should see a Plasma Rifle floating in the air a little bit above the ground. This is the Scarab Gun.
Use this video for help:
Start the level on Easy difficulty and cross the bridge. You need to lure the banshees into the tunnel, to do this, shoot at them while in the tunnel until one of them flies inside. Kill everything alive inside the tunnel (including allies) and make sure that the banshee does not fly away in the opposite direction (shoot at it). In the end, lure it into the tunnel outside and steal it. Once outside, fly up and you will see a large square in the middle of which the Scarab Cannon will be waiting for you.
Video:
https://www.youtube.com/watch?v=4FqL-GXSAx0&feature=player_embedded
First, set the difficulty to Legendary and at the Quarantine Zone level, pick up the satellite skull, which allows you to make high-altitude rocket jumps.
Next, we launch the Metropolis level we need, look for a grenade launcher and with it, reach the scarab and go out onto the bridge. At the last turn of the bridge (before framing the scarab), we find a box and move it to the beginning of the last turn, stand on it, aim at the column standing nearby and shoot at it with a grenade launcher.
Next we fly high near the bridge where our weapons are, we try to scrape against the bridge to slow down the takeoff, otherwise due to the strong takeoff during the fall we die in the air.
Video attached (ignore the ball) https://www.youtube.com/watch?v=PJC4_VJzkJo