This is a place for me to give you all skill I use daily on Halo 2.
No Scope help:
I No Scope at least twice per match I play. A little hint with the human sniper well have you sniping great in no time.
Look at the little zoom thing on the top of the sniper. If you look close enough, you'll see a little blue dot. That's your cross-hair. Use this in action and you'll no scope when needed.
This is proabally the most efficient Hint, Glitch, or Cheat I can ever give you.
If your playing Team Slayer, and their's wraiths, this is the perfect thing to do.
First, tell whoever gets the sniper to meet you behind your base. Second, grab the wraith and meet them their. Ram them with the wraith. Then tell them to jump when you ram them yet again. If done right the sniper well fly in random direction, (Mostly straight up) for a impossible to snipe sniping spot. NOTE: only works with either oversheilds, or Friendly Fire is off.
You can unlock the foundation MP map by finishing campaign mode on easy. there are also two other maps to unlock: Marathon and Conclusion. Try finishing harder campaign modes to unlock these levels.
Make Co-op and Campaign easier:
Once you have almost used up your sniper rifle, beam rifle, or rocket launcher (with 1 shot left ), trade with your squad mate. Once they have that weapon, they have limitless ammo for it and can help you out immensely with the more powerful weapons. There are two points to note: if you try and trade your weapon back from them, it will still have the same amount of ammo that it had when you gave it to them and the energy sword cannot be traded with human squad mates.
Note: I know many. I'll start with Beaver Creek:
When you are inside either of the bases in Beaver Creek, go to the back wall of the room where the bomb or flag is supposed to be. You should be able to grab the Plasma Pistol or the SMG on the other side of the wall and if you are playing Assault, you can then have someone stay inside the base and grab the bomb from the inside and get an easy score!
On the inside of any base, go under where the sniper is. (Use the teleporter sounds for help) By jumping while holding "X" you can pick it up through the floor. Bur say your playing CTF, All you got to do is jump on the bansee, (if it's not there, just jump) and jump again, holding "X". If done right, you'll grab the flag through the floor.
When Playing oddball, walk under the giant glass in the middle. (where it respawns) jump and hold "X" you should grab it through the floor.
Walk under the sniper, jump and hold "X"
Many XBL players know of the map Relic. Well, if you don't there's a gazillion foot tower. Many want to get on this tower, there is a way. First, you got to play just about the stupidest game version. Rocket's and over-shields. Use a warthog to push one of the metal shields over to tower. Get out. Stand on the end of the thing that keeps it standing. (looks like this: -----I ) Shoot a rocket at the top of the shield. You should go flying into the air, maybe high enough to get up there.