You dont get armour from the achievment:Marathon Man...
http://hubpages.com/hub/Halo-3-Armor
No, there is no armor in Halo 3 that has a knife in the shoulder.
when you activate them all you get the achievement called Marathon Man. It should unlock the armor called Security Shoulders
There is no Brute armor in Halo 3, only Elite and Spartan models.
go to http://hubpages.com/hub/Halo-3-Armor
As of now, it's 79. And Bungie will probably award you with something. Do you already have katana and marathon man armor?
you get all the vidmaster achievements on halo 3 and halo 3 odst
NO
recon armor
the same way in halo 3 because when you play halo 3 mythic it says your playing halo 3
there is no permanent cheats in halo 3. you need to unlock them by achievments. and, you can not get the flaming armor effect, it is only for bungie employees. in halo reach, buy the legendary package to get that armor effect.