Scarab boarding glitch
From Halopedia, the Halo wiki
The Wraith Boost Boarding Glitch is a glitch that can be performed on The Storm. When performed correctly, it will allow you to board the Scarab earlier.
How-to
Start at Mission Start. When you get to the area with the Anti-Air Wraith, kill all enemies but the Anti-Air Wraith driver. Melee off the side wings of the Anti-Air Wraith. Hijack the first Anti-Air Wraith using the Driving the Anti-Air Wraith glitch. Drive the AA Wraith into the next area and kill all enemies. When you see Judgment on the screen, save and quit. Then resume mission. After this, do not save and quit. Position the Anti-Air Wraith where the Troop Warthog was. When the Scarab's leg comes down on your position, press the LT button to boost and the Wraith should be sent into the air. Then exit the Wraith and you should be on the Scarab's deck. This may take a couple of tries and you may have to position the Wraith in the right position to get on top of the Scarab so if your position does not get you on top, press the Xbox Guide button and sign out. You should start where you last saved and quit. Sometimes, this method of boosting might overload the map and the Scarab or everything on the map but the Hornets and the Pelican should be removed from the level.