Triple wielding

Triple Wielding is a glitch interrupting with Halo 2's Dual Wielding system. As the name says, you wield three dual wieldable weapons at the same time. Though you don't shoot with them all, you do get 50% extra ammo, which can come very handy on big maps or on campaign maps with Flood or Hunters.

How to perform a triple wielding
1. Let's say that we want to triple wield three Needlers. First, have a Needler in your secondary weapon slot and a SMG (representing another dual wieldable weapon) in the first (in your hands).

2. Dual wield a Needler so that you end up having a needler in the left hand and a SMG in the right.

3. Now, trade the SMG for a Needler.

4. You have successfully triple wielded.

There is also a second method. However, this method gives you three weapons to cycle through, instead of just extra ammo. To do it...

1. Make sure you have at least one dual-wieldable weapon. For this example, let's say we have a Needler and a Battle Rifle.

2. Stand over another dual-wieldable weapon, such as a Plasma Pistol.

3. With the needler out, throw a grenade and while your arm is in the action, hold Y.

4. If you aren't host, it should say Picked up a Plasma Pistol, but you won't have actually picked it up (if you are host, you can't do it). As soon as you see that, tap Y repeatedly.

5. You will now be able to cycle through Needler, Plasma Pistol and Battle Rifle. To the host, you will just look as if you were dual-wielding a needler and plasma pistol.

On YouTube, there is a video guide that might be more helpful than what I just wrote, it can be found here