Unlimited Energy Sword
From Halopedia, the Halo wiki
Template:Ratings The Unlimited Energy Sword trick is done by playing a two part level. Then on the first level, grab an Energy Sword and use it until it is empty. Instead of throwing it away, keep it and use your other weapon. Then, after the second level starts, you will still have the handle. Even though you get the message saying "out of ammo", the game will mistake it for a sword and this glitched sword will have unlimited ammo.
The Best level to do this on is Arbiter/Oracle as it is easier to kill Flood that way.
Keep in mind that if you have a 0 charge energy sword when a level ends, and another weapon that is out of ammo, this will not work. If this happens, you'll have a certain set of weapons, depending on level, and character.
This does not work in Co-Op mode, for either player.
