Alternative 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.
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.
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.
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.
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.
Secret Cave: There is in level 5 a secret cave at the button of the map entrance. It comes out on the side where they are not expecting a side attack from that side and it shall be easier.
Carry 3 Weapons: You can carry 3 weapons after you have beat the game.
Defeating the Flood: In the later levels of the game you will encounter new enemies called the Flood. These enemies will be small at first, but they will attack and control anything alive. Use a shotgun on these baby Flood 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 Flood, and it will kill most of them in one shot. This is made easier by the fact that most of them carry shotguns.
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.
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.
Plasma Grenade: If your going to use a plasma grenade, try throwing the grenade on the alien where it sticks onto them. It will blow up on them making sure it will kill the alien. Also the aliens can do this to you if you don't move.
