I have made my theory about this on another site before, I did not interview any Bungie staff, neither work for them or even steal information. This is my theory about Halo 3 about the X button and the new weapons. As for Heimdal, don't spoil anything here such as the "Removing Helmet", I'm just explaining my oppinion about Halo 3. I could be wrong, but it's my oppinion. You may see in this quote where I mentioned about Heimdal, as said I placed this up on another website.
QUOTE(KrAzY)
My Theories on Halo 3
Ever since they removed the X button's feature toward to the left and right Bumper Buttons to reload for duals. Also the other features to interact such as turret, doors and vehicles will be used on the right bumper too. Well, although the bumper buttons is a new feature for the Xbox 360 a year ago, the black and white buttons are gone. That means that you won't be able to switch grenades, or use a flashlight nor camoflauge anymore, they can't even be used on bumper buttons due to reloading and interactions which was used on Halo 2 that was compatible with the Xbox 360. The bumpers was made for reloading for a better experience, because they can't move the camera while reloading or interacting the environment, and it can help to reload a specific gun for dualing than combined. But what is the X button for? What will flashlight and grenade switching be used on?
There's somebody I know who works for Bungie in a StarCraft Map-Making site which he had experiences of modifying StarCraft's map-editor, he named it StarForge. While hired for Bungie, he had an interview that he had to introduce himself and his experiences. He said the X button is to take Master Chief's helmet off, but what about the Arbiter who is an elite? Or the new character? Since there is the new "spike" grenade that sticks anywhere and explodes into spikes like needlers, and another grenade shown in a trailer where Master Chief throws it on the floor and gives a defensive bubble shield, there's probably a new way they could switch grenades. First, there is no black button. Second, who wants to push the Black Button three times to get a specific grenade? In my oppinion, I think they will be using the D-pad for grenade switching, one will be for frag grenades, another for plasma, and another for Spike and maybe another for the shield bubble. Some say the shield bubble grenade is the X button, but I think the X button puts up flashlight, camoflauge or maybe beserk if Brutes are a new race for multiplayer. Camoflauge is the main ideal for the Arbiter levels, you really have to stay stealthy and it part of the game big time in Legendary. As for I know, the D-pad is completely useless in Halo: Combat Evolved and Halo 2 itself, they might probably use it for the first time.
There is a second theory for the X button. In Halo 2, they use the right thumbstick to click to zoom in, if the weapon isn't a zoom-in weapon, it would show binoculars. The binoculars is actually a useless feature in my oppinion, sometimes it just distracts you but it's just a way to find somebody with an SMG. They might push the right thumbstick as the flashlight feature since it's part of the camera. It could also be the button to activate the camoflauge. The X button for all I know could be something new, it could be the sprint button featured in the second Halo 3 video shown in Monday Football or to gain consious while dead. As in Tom Clancy Games or some sci-fi games use night vision, thermal vision to view the battlefield. Master Chief has a helmet with an orange glass, maybe it could be a vision feature. Ever since there are brute weapons, maybe it can make the feature of secondary fire such as grenades and they could still use the left trigger to shoot frag, plasma, spike or the shield bubble. It may change the fire mode, and you get to launch some explosion with the right trigger. There are so many possibilities I have yet to think about, but I'll have to go with my first theory over my second one because it seems reasonable.
As for the Spartan Laser, it's no brute weapon. As for the grenade that protected Master Chief, it's no brute weapon as well. As I mentioned about the fourth grenade being the fourth button on the D-pad, what if there is another set of weapons made for Spartans? One is for humans such as Battle Rifles and Assault Rifles, another for the Covenant used by Elites, Grunts and Jakals while the new one for brutes and I assume they still use the Brute Shot. There could be another set of weapons just for Spartans like the Spartan Laser and the bubble shield grenade, this gives me a theory of the set of weapons: Blunt Bullets and Explosives, Plasma that burns, Spikes that are brutal and Lasers and hi-tech features for Spartans like the Spartan Laser. The Spartan Laser is no brute weapon as said, it shoots a very small laser very affective against vehicles with no use of spikes. If the brutes have new vehicles such as the Brute Ghost, there could be new vehicles for Spartans. The UNSC probably invented some ways to give Spartans a big advantage to survive.
As for I know, a true next-gen sequel isn't all about graphics and additional new weapons, I think Bungie gone intense by bringing four sets of weapons. The brute weapons may change experience, but what if they added the Spartan weapons if the Spartan Laser existed? I don't think the Spartan Laser goes to the Brute category. Halo: Combat Evolved has a lot of human weapons and vehicles while a few for the Covenant. In Halo 2, the Covenant has been featured with a same set of weapons like Carbine to Battle Rifle and Plasma Rifle to SMG. I think in Halo 3, they will have another set of weapons like the brutes, but as well for the Spartans. It is called "Spartan Laser" for a reason, it has no relation to the human, covenant nor the brute weapons. Maybe Bungie is trying to make us think hard, just like my theories on the X button and how the Brutes isn't just another set of weapons. If I was right, I might as well be damned but I highly doubt it. What do you think?