To get a different and longer ending movie Halo, beat the game Legendary.
Infinite Grenades:
To get infinite grenades, scorpion, and ghost in multiplayer- Go to the multiplayer screen: go to edit game types: In that menu you will have the option to make up your own game type.
Unlock 2 new guns:
Beat the easiest setting then on the hardest in 3 hours to unlock 2 new guns
Pistol-Whip It Good:
Never underestimate the power of a well-placed melee attack. Smacking someone or something with the butt of your gun is great fun and immensely effective
Get the Drop on the Dropship:
When a drop ship unloads aliens, the next drop ship will hover in the air. If you take your sniper rifle and zoom in on the sides where the doors open, the targeting cursor will turn red. Fire once or twice and the alien will plummet to the ground.
Best Anti-Flood Weapon:
The combat shotgun is the best weapon when you fight the flood. It'll take them down in 1 or 2 shots. Forget the assault rifle or the plasma weapons shotgun is the way to go.
Flash Flood:
When you encounter the race known as the Flood, turn your flashlight on and point it at them. The large one will stop running and jumping so that they are easier to shoot. But, if you raise your gun to reload, turn away from them or take the light off of them in any way, they will resume running around and try to kill you again. Although the creatures infected by the flood stand still when you point the flashlight at them, they may still shoot if they have a gun, so kill them quickly
Defeat the bus in Face Off 4.
Increase boost:
Drive on the wrong side of the road to keep increasing your boost. This can also be done by driving in the center of a double lane.
Drive in the wrong side of the road and use the turbo when you get it. After it is gone, your turbo will either be full or half full.
Full bonus:
Drive a perfect lap (a lap without any accidents) and your bonus will be automatically filled.
Face Off option:
Successfully complete championship mode once to unlock Face Off 1 against the Roadster.
Roadster:
Defeat the Roadster in Face Off 1 to unlock it and Face Off 2 against another car.
Towtruck:
Play in championship mode until you unlock Face Off 2 in the special options screen. Defeat the Towtruck once to unlock it.
Saloon GT:
Defeat the Saloon GT in Face Off 3.
Quick start:
Accelerate immediately before the "1" fades during the pre-race countdown to start with a slight boost in speed.
Interstate: No traffic:
Select the Interstate course. When the race begins, drive over to the other side of the highway into the HOV lane (brown with white diamonds). Look over the barrier that separates oncoming traffic. There will be no traffic on the other side.