General Level Hints

If you see plasma, or frag grenades sitting on the ground in the mix of combat leave 
them there. Wait until a group of Ailens come near them and toss what ever kind of 
grenade you have and it will detonate your's plus the ones sitting on the ground and 
they will go off like an Atomic Bomb so run.
Submitted by Dapantha33 
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Sentinels: 
Use a plasma weapon to take down sentinels in one hit(7-10 level).
Submitted by seaque at qwest.net   
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If you beat any level on legendary you will get new enemies.
Submitted by jennifer
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Levels 1-10:
With the plasma pistal hold down your right trigger.This will charge up your gun. shot 
the jackels sheild and it will shut down,deactivate,what ever you want to call it. it 
will be easier to hit them.(shot them quickly because the sheild will active again) 
Submitted by gdfan89
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On top of 342 Guilty Park: 
When your evac dropship is about to let you out, or when you can see inside your ship, 
throw a grenade.This will prevent you from getting out of the ship. You'll take off with 
evac and will land on top of 342 GP. Get out of the ship and you can walk around up there. 
It's really cool, all the trees are 2D. If you keep on going you'll find a soilder without 
a gun that is just standing there. It's pretty weird. Normaly just before you get to the 
large structure and see assalt rifle fire (it won't do that while your up there). Jump 
off the cliff down to the large structure and see that they are floating assaltrifiles
that fire and then drop.
Submitted by Scsbuzboy at aol.com
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When facing the big flood in stage 343 Guilty Park and the rest of the levels, when you 
kill them once dont leave them behind because the get back up for a second and final 
attack!
Submitted by kobra7146 at aol.com
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At 343 guilty spark, as soon as you see the grunts and jackals running, push the grenade 
button as fast as you can until you see yourself throw a grenade. When you do that it 
will let you stay in the dropship and it will take you up on a hill. Then that's where 
you get out. Go down the hill to your left and go to the right.It will take you to the 
building that you need to be in. In the door, you will see assault riffles firing, but 
no marines or anyone behind them. 
Submitted by dogman308
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When in the silent cartagropher level go down the passageway to the locked door with 
the warthog. Do a tailwhip and make sure the driver's seat is facing the door. Get out 
as fast as you can and you could get past the door befor it locks. Don't be alarmed 
about you can't get back out. There are still checkpoints and it will open up when you 
have found the map. 
Submitted by bigmac618
PS: The sword elite will not attack you