EGM is supposedly releasing another Halo 3 special in their august issue and the following information is meant to be a leak from it. I have no clue whether any of this is true or not so dont shoot the messenger.
New Gear:
Flare - It's a flashbang. Seems Forerunner in design, definently the unknown grenade type.
Mauler - Dual-wieldable shotgun. Brute weapon, mandatory blade randomly sticking out the bottom.
mavity Hammer - Based on Tartarus special toy. Can act like a sword, but mostly used for area attacks and physics based fun. Sends vehicles and grenades flying. Has a shockwave-type effect.
Regenerator - Equipment. Like the power drainer but opposite.
Radar Jammer - Equipment. Causes radar to go crazy with false positives. More importantly though, described as "mostly" useless in the campaign. Yea, okay I guess it's just a turn of phrase.
Positional Shield - Equipment. Pretty much exactly like the ground shields in Halo/Halo 2. Not clear whether or not it's permanent or whether or not it lets gunfire through one side.
New Vehicles:
Prowler - A Brute Spectre. Looks amazingly badass.
Hornet - UNSC helicoptor only seen in Campaign mode so far. Appears to carry passengers, but God knows how, seems to expose them more than the Mancannon does.
Elephant - Described as a Jawa Sandcrawler, it's essentially a UNSC Scarab. A dozen soldiers can ride it, it can house a Mongoose in it's belly, is driveable, has a turret, can respawn troops, and holds both the flag and cap point. Only available on Sandtrap as of right now, and is only thing specifically mentioned not to be included in Forge.
Campaign:
Online Co-op - ?
Brutes - They stay towards rear, commanding others in encounters. Berserking is gone, but they will do a monkey charge if stripped of their technology. Chieftains come with Grav Hammers and the same invincibility power Tartarus had. Oh and they can use jetpacks.
A.I. - The monkeys can now climb, along with the rest of the Covenant.
The Arbiter - Nothing. "No Raiden moment." Campaign is 100% MC, with Arbiter in tow for Co-op. Whether this means Arbiter won't be selectable solo at all or rules out 4 player co-op is unknown.
Encounters - "There's an encounter at the end of the second mission that you play that has more enemies allies than the entire first mission of Halo". Claims less drastic distinction between the Now I'm Exploring This Corridoor, Now I'm Blowing Up Vehicles parts.
Lighting, Sound, Music, Graphics in general - Godly. Around 40,000 voice clips too. Cursing used to indicate status.
Metagame - Played solo or co-op, score based on player performance and active hidden skulls. Presumably difficulty level too. Mentions stat collection on bnet but not the all important LEADERBOARDS.
Multiplayer:
LOCKOUT REMAKE - Not really. Map's name is Gaurdian, Forerunner place hanging in the jungle. "This is not a port of Lockout". Maybe he's lying? Supposedly Lockout influenced, it's really hard to read the section on it. The screen of it has the double level and catwalk thing going on but seems much, much larger.
Game Modes - A good amount spent on the customizeable gameplay modes. mavity, spawns, move speed, and even stuff like immunity while within a King of the Hill circle are customizeable. Lists stuff like Hamster Crack and Hammer Time, but it's not clear whether these are actually preset modes or just ways of messing with options in Custom games.
Sandtrap - Vehicles on a goddamn 15 second respawn timer. Not really clear how the vehicle spawn locations will interact with moving the Elephant around.
Elite model - Larger than Spartan but not so much to gimp yourself. Head seems to have been raised much higher although it definently still seems longer than the Spartan domes.
Invincibility - Based on Tartarus green haze of don't waste your ammo, allegedly rare in multiplayer.
Forge:
You can turn your Spartan into a Halo Monitor and back again. That's pretty much it. Full control over a map's spawned items except for the Elephant. Multiplayer, although player count unknown. Everyone gets a Monitor. Create your own gameplay, or whatever that stupid buzzword is. Divergent, or something. Will track Spartan's stats for goal based play, although won't have any rules enforced.
Marathon:
Speculation about the terminals, no new info. But the magazine says Marathon should be on XBLA "now". Which should correspond to sometime near August 11th.
Story Stuff:
If it's purple, kill it - Grunts switched sides again apparantly. Hunters may or may not have. Frankie's already confirmed that the Arbiter is the sole elite in the first mission. Bungie has made a specific point about being translucent on who the bad guys are, no leap needed to conclude the giant plant monster is connected to the parasitic zombies.
ARG - I'm sure this is probably obvious to anyone keeping track of it, but the ARG definently connects to the Halo 3 storyline.
Afrika - Not much revealed we don't know about. The Covenant are ripping up the Earth to get to the Ark. Appears they've found it by the end of the third mission (which is where the E306 trailer should fit).
Scarab - The next level has you and a dozen marines chasing down a Scarab on the backside of Mongooses firing rockets at thing. Scarab is unscripted A.I.