Save Marines on Sacred Icon
From Halopedia, the Halo wiki
This is a glitch that allows you to save some anonymous Marines on the Halo 2 campaign level Sacred Icon.
Procedure
In order to Save Marines on Sacred Icon, you will need to acquire the Sputnik Skull. Play the level until you get to the part where you hear the Marines saying something along the lines of, Marine Sergeant, "Proceed to the objective, we'll hold out as long as we can." Marine Pvt., "Uhh Ahh! Get it off me!", "Suppressive fire, Suppressive fire!" At this point, grenade jump across the gap to where the Marines are. This is very difficult to pull off, as a single hit from any Flood forms will kill the Marines. However, if some manage to survive, you will notice that, unlike in the level Great Journey, the Marines are your enemies. This is the only way to fight Marines without betrayals or mods as the Arbiter in Halo 2, the easy way to save them is by shooting the Flood. It is recommended to take their Sentinel Beam because it has a range advantage, allowing you to take out the Flood rather very easily.
