Secret Gravity Hammer on Midnight

The Secret Gravity Hammer on Midnight is a Legendary difficulty-exclusive easter egg found in the Halo 4 mission Midnight. If performed correctly, it spawns a second Gravity Hammer for use in the mission.

Walkthrough
Play through the mission normally until the checkpoint titled "OLD FRIENDS", also known as Rally Point Charlie. Then, fly through the conveyor lift as normal and pick up a LightRifle and Binary Rifle with maxed out ammo for all weapons (108 and 6 reserve rounds, respectively). Insert Cortana into the platform's terminal as normal.

The easter egg will only work on the rightmost platform, so get to there. Here, Promethean Crawlers and Watchers will spawn. Use the LightRifle on the Crawlers, making sure to not waste too many shots. Always make sure to destroy the Watchers with the Binary Rifle so as to conserve LightRifle rounds for the next set of enemies. Climb up the ramps to the top of the pillar and activate the light bridge.

Eliminate any and all remaining Crawlers and Watchers in the area, making sure to conserve Binary Rifle ammo for the Knight Commander who spawns in to guard the next terminal that Cortana must be inserted into to break the Composer's shielding. Be careful of the Knight Commander, for he is capable of a one-hit kill with his Incineration Cannon.

When the Knight Commander appears, headshot him twice with the Binary Rifle to lower his shields and then destroy him with a few headshots using the LightRifle. Once he is disposed of, immediately grab his Incineration Cannon. Using any other Incineration Cannons from earlier will not work for this easter egg.

After grabbing the dead Knight's Incineration Cannon, face the next terminal, but turn around, walk back up the small ramp, turn right, and jump onto a pedestal. There are eight smaller pillars to destroy with the Incineration Cannon; the first one should be in plain sight, below the smaller pedestal. Shoot an Incineration Cannon round into the pillar to destroy it. Do not stand too close, though, as that exponentially increases the risk of suicide, especially with the weapon's explosive submunitions.

The second and third pillars are close to where the terminal is, to the left of a larger M-shaped arch. Shoot them separately. There should be one last round remaining in the Incineration Cannon before it runs out.

The fourth and fifth pillars are immediately on the right side of the pillar. Blow it up, and there should be a message on the screen saying "Out of Ammo". Run back down to the lower level of the platform, and there should be an opening to a small room with a weapons cache containing an Incineration Cannon, two Pulse Grenades, and four Boltshots. Grab the Incineration Cannon here.

There should be four rounds in the Incineration Cannon now. Climb back to the upper level of the platform and return to the M-shaped arch where the Knight Commander was killed earlier. Now destroy the fifth pillar and turn right to find and demolish the sixth and seventh pillars, which are close by. The eighth and final pillar is off to the distance and is not located close to any of the previous pillars. Destroy it with the eighth and last Incineration Cannon shot, but make sure to use its scope so as to not miss.

Once the final pillar explodes, the Gravity Hammer should immediately spawn in front, falling onto a small pedestal. Feel free to take it for use later on in the mission.