Handheld scorpion cannon
From Halopedia, the Halo wiki
After exiting out of Outpost Tremonius into the outside area, head to the ship debris on the right. Use the grappleshot to get to the ledge where a pair of turrets are located. Make your way to the turret farthest from the entrance of the outpost. Get on top of it and go to the end of the turret. You should see a prompt to pick up a weapon. You can now use the cannon.
As a glitch weapon, it possesses unusual characteristics unlike any other weapon in the game. The weapon itself is completely invisible, and the crosshair is the same as the one displayed while driving a Scorpion Tank. Whilst holding the weapon, Chief will be stuck in a semi-permanent idle animation with his hands outstretched as if holding a weapon, appearing to slide around in a standing position instead of properly walking or running. Additionally, when mounting any vehicle's gunseat, although Chief will be shown entering normally, upon sitting down he will immediately return to his standing position. The cannon's aiming range is also noticeably smaller than the actual camera range while riding this way, unlike conventional weapons, particularly on the rear seat of the Mongoose and Gungoose, as the projectile will seemingly only fire directly opposite the vehicle, regardless of where the player is aiming.
Most of the player's abilities are preserved while wielding the cannon, however sliding and ledge vaulting are not, so quick swapping must be utilized in order to make use of those abilities.
The projectile itself is odd in that it generates from the center of the screen and from a much lower position than other weapons. Though mostly mundane, this can actually detriment the weapon's ability to be used from high ground as ledges can easily catch the projectile, resulting in it exploding prematurely. This can be circumvented by jumping prior to firing. The explosion cannot harm the player directly, so using it in close quarters is viable, provided no other explosives are nearby. The weapon has a very slow rate of fire but possesses infinite ammo in turn.
Care should be taken if the player wishes to keep the weapon on them; dropping the weapon, either manually or by swapping it for another, will result in it vanishing completely, requiring the player to replay the mission Outpost Tremonius to obtain it again. Switching to the secondary weapon will not void the cannon, and likewise, the secondary weapon is able to be swapped out without affecting the cannon.
- Brian Jarrard confirmed that it was indeed a glitch and not an easter egg via Twitter.
- This confirmation coincided with the weapon's temporary removal from the campaign. Though this was later rolled back following a heavy amount of backlash from fans.