"Here is a complete guide of enemies and there weaknesses or just an easy way to kill 'em.
Coventant: The normal aliens looking things, here's the guide.
Grunt: Little freaks that stant 5' tall but look 3'. Just whack 'em and they usually die ,1-2 whacks. Also, just stick 'em wiv a plasma grenade. They run to thier pack, including 1 or 2 Elites and maybe a few Jackles and some grunts, unless you killed 'em all
Jackle: Lizard type things with energy shield atached to thier wrist, and snipers. Get close to a snipe-jackle, they'll drop thier beam rifle and run away with only a plasma pistol. Either way, shielded or unshielded just give 'em a good whacking or, with the shielded one, throw a grenade low and they won't see it. You know the rest.
Elite: A four-jawed Covenant that is a brave warrior and leader. Blue is the Minor, red is the Normal, and the gold is the Magor. The golden guys have energy swords so watch out. Either stick 'em, shoot em wiv a couple rounds of smg or charge a plasma to deplete thier energy shields like the Chiefs and shoot 'em a little.
Hunters: Big Dumb Ugly and Furosious is a qiuck dicription of the Hunter. They are pretty easy if your are good enough. On some levels, you can sneak to a place they don't see you, and F.Y.I. this pretty much only works with the sniper, unless you're really good wiv a BR(Battle Rifle). Just snipe 'em in the orange flesh a couple times. Oh and the Hunters come in pairs so you need another good weapon, too, in case one charges and you can't snpie it. Another way is stick it a few times or resort to just shooting the crap out of them, if they have crap in them.
Drones: A bug like speiceies that are new to Halo Veterans, unless you're a Halo 2 Veteran. Just shoot 'em wiv a BR, they'll just fall off the wall they are on onless they are flying, dead.
Brutes: Giant Gorrilla things that, like the Drones, are new to Halo Veterans. These are like Elites, but without the energy shield so just blow 'em up or shoot 'em
Prophets: You'll see 'em when you get to the level Regret. There's only one way to kill them.
The Flood: Deformed Elites and Marines, these guys are freaks.
Infection Flood: Those little ball Flood that when the hit you, explode and do a small emount of damage. Any bullet with kill them, but thier fragility is made up for their numbers when they attack. Just shoot 'em with an smg or plasma rifle.
Carrier Flood: They with burst when they get near you, or unless you shoot them, but if they burst by you, it will deplete you're energy shield and then out of the Carrier Infection flood will attack, and that's why they are called Carrier Flood.
Combat Flood: Deformed Elites and Marines, these will attack anything. They can carry any weapon and there mutant limbs are good melee weapons.the easiest way to kill them is to shoot them wiv a shotgun. Oh and sometimes they play dead. When you arn't looking they'll come up and attack, or if you wait long enough will get up even when you are looking at them.

So go kill stuff!" - Crazy Squirll

"on the third level (metropolis i think) at the start when u are on oer near the middle of a bridge there should be some banshees around. do not shoot them! then get close to one and hijack it as quick as possible then go as fast as u can near were other banshees are flying which is near the first tunnel and then go above them and keep flying and then land somewhere on top of the place and then there should be a plasma rifle floating there in mid air. it does as much damage as a scarab and is an awesome weapon. it is very hard to get cos i only did it once but u hav to go really fast though it is really hard to get but it rocks." - awesome killa