Hint: Alternate ending sequence:
Successfully complete the last level of the game in campaign mode under the legendary difficulty setting. The new ending features a human and alien fighting hand to hand. The human will say "Its over", and then they hug because they know the explosion will kill them both.

Hint: Alternate dialogue:
Playing under the legendary difficulty setting introduces new dialogue not heard in other modes. For example, after being massacred by a force of Grunts, Jackals and Elites, one of the grunts asks, "Can I have his helmet?". Also, your fellow Marines seem to be a bit more chatty (as well as profane).

Hint: Final ending scene:
Successfully complete the game on any difficulty setting and wait for the credits to end. The game will show the Monitor fly across the screen and laugh.

Hint: Faster reloading:
To reload most weapons faster, press X and shortly after that press B to melee. Note: For the shot gun this will cause you to stop reloading all together.

Hint: Extra ammunition:
If you shoot your fellow Marines you can pick up their ammunition. Make sure to only kill a straggler unless you are prepared to take on all of the Marines. They will turn on you if you kill more than one of them.

Hint: Extra shotgun ammunition:
Take a shotgun that has 12 shots and 0 clips. After you shoot it a few times, you should be able to reload manually. You can do this about ten to twenty times.

Hint: Faster Warthog weapon use:
This trick works best in multi-player mode. Drive the warthog in a straight line. When you see an enemy, jump out of the Warthog. Tap X repeatedly and sidestep to the right. If you are quick enough, you will exit the Warthog and jump on the LAAG gun without stopping, while the Warthog slows down. This also works well on ice, because you keep sliding.

Hint: Defeating Covenants:
When Covenant dropship is getting ready to unload a group of Covenants, throw a grenade into the door as it opens. The blast will kill several of the enemies since they are all in one area.

There are places (especially in the first level) where a groups of Covenants are, waiting for you to barge in and start shooting. If you can, sneak to the aliens and throw a grenade into their midst. It is best when a plasma grenade sticks to a Grunt, because he will run behind the rest of his companions. One simple grenade can take out five Covenants.

When trying to kill Covenants, jump over them (so you can look at their back) then shoot or hit them with the butt of your gun.

Hint: Defeating Elites:
Find a needler and waste a clip on an Elite during the early levels. This will take out the Elite and the gathered needles form grenade-like explosions, injuring if not killing anything near the target.

Hold R to fully charge a Covenent energy pistol. You can continue to hold the charge indefinitely. Find an Elite and blast him. Depending on the distance to him, he will sometimes flex and get angry. When he does this, walk up and punch him with the pistol. On the easy difficulty setting, he will die immediately.

Hint: Defeating Flood types:
Do not try to take out any Flood types with a sniper rifle. It will simply go through their bodies without killing them. The weapon of choice is the shotgun. You can take them down with one shot. Remember, the closer they are, the faster they fall.

On the small crawling Flood, use your assault rifle in short controlled bursts. Once one pops, it will also pop the ones nearby. Save shotgun and pistol ammunition for the working class Flood to drop them fast. It is also a good idea to hit them with your gun after they fall to make sure they are dead. On the fat Flood, use the shotgun to pop them, then clean up with rifle.

When you first meet the Flood, they will outnumber you in groups. For the large Flood, use a shotgun, rocket launcher, or most importantly, a fragmentation grenade. Do not use a plasma grenade because they will run towards you and kill you.

When you get attacked by the Flood, after you make them fall down the first time, shoot their head off while they are on the ground. They will not get back up.

Most of the Flood attack you with weapons and strong melee attacks with their arms. Some of the combat form Flood are harmless. They may chase you, but they cannot inflict any damage. You can tell that they are harmless by noticing that they have no arms. Do not waste ammunition on these harmless flood -- just melee attack them. Be careful not to mistake the harmless for the harmful types.

To end all Flood types quickly under the easy difficulty setting, crouch down and shoot their legs with the shotgun. You do not have to crouch yet when they are swarming on you -- it seems to confuse them. Stay crouched, pivot, and fire. Also try to alternate shooting, crouching, and shooting, etc.

Melee any Flood that are too close. This will buy time to shoot other Flood and save your Shield. This also works against jumping Flood.

When battling the Flood, use human weapons such as rockets, frag grenades, pistols, assault rifles, and especially shotguns. After you have knocked one of the enemies down, hit them with the butt of your gun to kill them permanently.

Hint: Fun with the Flood:
Use the human handgun to shoot the weapon out of the Flood's hand, without shooting off the limb. The Maw is a good place to try this.

On any level with the Flood, kill one of the bigger ones. If you look down at it, it may have one of those messed up arms. You are able to shoot the arms and the head off.

Hint: Defeating Flugs:
In the later levels of the game you will encounter new enemies called Flugs. These enemies will be small at first, but they will attack and control anything alive. Use a shotgun on these baby Flug as they tend to group in large numbers. By using the shotgun it will send a storm of bullets and kill most of them that are around. Use a shotgun on the possessed Flug, and it will kill most of them in one shot. This is made easier by the fact that most of them carry shotguns.

Hint: Defeating Grunts:
When the Grunts are sleeping you can beat them to death with the butt of your gun without waking up any of the other Grunts. You can usually kill a four to seven of them before an alien spots you. They start sleeping in level 5, Assault on the Control Room. Just remember not to shoot or they will wake up.

Hint: Defeating Hunters:
Normally Hunters are the hardest Covenant to kill, due to their powerful armor and shields. However, even the strongest armor has weak spots. If you look at their necks or backs, you can see an orange spot. Aim for it. One shot with any gun will kill them if you hit them there.

The best way to kill a hunter is to use a sniper rifle to zoom in on the orange spot.

When you see a Hunter, you can shoot them in the head with a sniper. It should kill them instantly.

If you are being chased by a Hunter or an alien with a sword, run backwards while facing the alien. Jump when they try to slash you. Throw a plasma grenade at the alien and it will stick to him. Turn around and run in a zig-zag pattern to make sure he does not catch you in the explosion.

If you are playing cooperative multi-player mode, have player two run in front of the Hunter until his back is turned to player one. While the Hunter is trying to turn player two into mush, have player one run up to the Hunter's back and melee attack the orange spot. The Hunter should die with one hit.

You can kill the Hunters in a head-on assault. Get in close and use the pistol or shotgun. Aim for the head holding down the trigger. Your first shot(s) will knock back the head, exposing the unarmored neck. One shot in the neck and they will die.

An easy way to kill a Hunter is to hit them with a vehicle. If you chase them with the vehicle, they will try to dodge.

Throw plasmas grenades on them. It may take a some practice to get them stuck on a Hunter, but with two grenades, he will probably be dead (depending on the difficulty setting). Note: Do not stand too close or you may be blown up, and the plasma grenade will not stick to his shield.

Hit Hunters with a melee attack. They will put their head down and the orange spot there can be seen. Melee attack that spot to kill them faster.

Shoot a Hunter in the orange spot in his midsection with a shotgun at point blank range. This will kill it on every setting, including legendary.

If sniping Hunters is not fun for you, try this. Approach a Hunter, being sure to avoid any blasts from his fuel rod cannon. Shoot him a few times to make him charge, and as he starts his melee attack, quickly sidestep around him until you face his back. If done correctly, you should be looking at his back before he finishes his attack. When you are looking at the back, shoot it as many times as you can before he turns around. For even more fun, charge as you are shooting his back and press B when in range for a melee attack. The best gun for this attack is the shotgun, but the assault rifle also works..

Hint: Defeating Jackals:
Use a photon weapon to destroy a Jackal's shield quickly.

When you encounter a Jackal, run up and hit it with your weapon or get out a gun that uses bullets, not energy.

When you are a far way away from Jackals and have a sniper, they will sit in the defense position and leave very little uncovered. You will notice that on the right or left is a small notch in the shield. Aim for it and the Jackal population will be severely decreased.

If you are having trouble killing the Jackals because your ammunition deflects off the shields, just get close enough and melee attack them from the front. This can save parts of your shield and a lot of your ammunition.

Hint: Easy kills:
To kill someone, it is often easier to run him over rather than shooting him. If you shoot him, it will take a few hits. If you run him over, it will take only one hit.

Hint: More gore:
After defeating any of the aliens, especially the Elite, go over to the dead body. Repeatedly press B. After a few hits the area around of the dead body should have more blood around it. The Grunts and the Hunters will not put out as much blood as any other alien.

Hint: Easy Banshee kill:
Wait until a Banshee is directly above you, then shoot it in the belly with your shotgun. On the easy difficulty setting, it will explode with one shot. Moving forward when you do this can keep the wreckage from falling on you.

Hint: 343 Guilty Spark: Active camouflage:
Just before the area where the Covenant are guarding the entrance to the facility containing the Flood disease, you will see a large rock on the right side of the screen. Jump above the rock to find an active camouflage hidden behind a bush -- look carefully.

Hint: 343 Guilty Spark: Shortcut:
Tap X to get back in the Pelican. It will fly onto a ledge. Walk along the ledge in the direction you are going to end up above the tunnel where the Marines are fighting. Jump down to the tunnel, then continue the level.

Hint: 343 Guilty Spark: Hidden area:
This trick works in co-op multi-player mode and perhaps in campaign mode. When you are about to land in the Pelican at in the beginning of the level, start throwing grenades as fast as you can out of the ship. When you are around your fifth, sixth, or seventh grenade, you will get hit with a grenade, but not take any damage. When you are out of grenades, wait in the ship. It will liftoff the ground and fly you to a strange area with two dimensional trees. You can see the edge of the level. You can get back to the normal level easily, by jumping down from where you are.

Hint: 343 Guilty Spark: Hidden Marine:
Go to the two dimensional place and keep walking straight until reaching a sort of wall. Walk along the side of it, then take a left once you get past it. Keep walking straight. You will notice a figure in the distance. Keep walking forward and it will turn out to be a Marine.

At the start of the level, during the opening FMV sequence press the grenade button before you get out of the Pelican. If done correctly, you will stay in the Pelican. It will land on a nearby hill. Press X to exit the Pelican. You will be able to walk around on top of the level and see a group of two dimensional trees and a marine. He will not talk to you unless you shoot him. If you look down, you can see were you are supposed to be and the structure you are supposed to enter. Jump down there and look in to see floating assault rifles.

Hint: 343 Guilty Spark: Deadly bubbles:
When you get dropped off by the Pelican, run to the front of the ship. In front of the ship you well see a rock. In front of that is two trees. In front of the two trees is another rock. If you go to the left of the rock, you are in very deep water. Duck to get underwater. If you shoot, you will see bubbles. If you shoot at the lily pads, the bubbles will kill you.