Spartan Laser Glitch
From Halopedia, the Halo wiki
The Spartan Laser Glitch can only be performed when climbing your way up to the top of the Control Room on the last level of Halo 3, Halo. As you are climbing up to the top, you will see Sergeant Major Avery Johnson on the far left mountain side, helping you with his M6 Spartan Laser.
Unlimited Spartan Laser Ammo
In order to obtain the Spartan Laser with limitless ammo, you need to go to the last level of Halo 3 (Halo) and start at the very beginning. Keep playing through the level until Sergeant Johnson makes contact with you. Continue onward until you reach the second Ramp on the outside structure of the control room. Get a battle rifle or a Covenant Carbine and perform a head-shot on him (be sure to get him to position where he should fall off the cliff.) Once he falls off the cliff, he should respawn after falling off (It is also worth noting that if there are any nearby Flood Combat Forms or the like, then he won't respawn, so be sure to clear them out before moving on.) But before he respawns, take his spartan laser away quickly and check to see if his spartan laser ammo count reads 21 or higher. Anything 20 or lower will cause the glitch to fail. If indeed you do get a spartan laser with an ammo count 20 or lower, make sure there are no weapons near Johnson so that he may take out another spartan laser among respawning. Wait for a minute before you kill him again. Killing him immediately after respawn will make the Arbiter and other allies to assume you are a traitor and turn against you. After killing him again, take his new spartan laser and it should have a high ammo count. You may now use the Spartan laser as many times as you want but be sure you leave it behind before encountering the battle with 343 Guilty Spark, otherwise when you kill 343 Guilty Spark, you will lose it.
Method 2
Wait until you open the door and prepare for the final battle. Johnson appears inside the hallway behind the door. Wait until you get Gravemind's message. THIS IS IMPERATIVE! If you kill Johnson before this, the Laser will NOT have Infinite Ammo. After you kill Johnson, take his laser. If you leave another weapon behind, he will take that instead of a new laser. If in Co-op, have the second player take the ammo. Kill Johnson multiple times to get multiple Lasers.
On Legendary, it is observed that if you kill Johnson multiple times, leaving multiple lasers on the ground, after the 343 Guilty Spark battle, Johnson will still be alive with you, and his old Lasers will be on the ground, still with infinite ammo. It is also noted that Johnson can, in this way, be infected by Flood. If he does not, he will disappear at a Loading...done screen.
Note: The first Spartan Laser he normally carries does not have infinite ammo. All lasers afterwords do. Noted that the lasers have obscenely short amounts of battery in example '1' '3' and '27'.
Glitch 2
While charging up the laser, keep spinning around until it fires. When it fires, it will be a bigger than usual shot, though it is very hard to aim, because you are "spinning".
Glitch 3
When in Forge, charge up the laser and when the tick on the crosshair gets to the end of its line and you see a red glow on the muzzle go into the Editor Mode by pressing up on the D-pad. If you did it right, you can aim at an enemy and when you come out of Editor Mode it will instantly fire your laser. Keep trying until you get it right. This method does not use any of the laser's energy. Note: Occasionally, doing this will cause the laser to fire multiple shots in rapid succession.
Trivia
- If you are holding the infinite ammo Spartan Laser, you can pick up the normal Spartan Laser and hold one in reserve and one as the main. Though this is completely pointless gameplay wise it is a nice glitch.
- Sometimes Johnson does not get a new Spartan laser upon revival, this causes an odd glitch within the 343 - Johnson scene. Johnson looks up, doesn't fire a weapon (He doesn't have one), yet Spark goes flying as if he has been hit by one. Also, If you leave another weapon on the ground (i.e. Carbine) then Johnson will pick it up, but during the 343 Guilty Spark Battle, after he shoots Guilty Spark with the "Spartan Laser", you can walk up to him and the screen will show "hold RB to take [whatever weapon you gave him]"
