Tired of trying to or simply can't Shield Bump?
Then try this solution as an alternative method of beating the Par Time of 15:00 for the level Keyes - I would actually highly recommend this method before attempting the Shield Bump method simply because you don't have to be pixel perfect - there is a greater margin for error while still being successful!
I was getting ready to attempt the Shield Bump method and there are several video tutorials out there but the comments on the videos and here on TA were discouraging until I stumbled upon another glitch - the Flood Bump!
It took me about 20 minutes of trial and error until I finally got it to work and I managed to finish a Legendary Speedrun in under 3 minutes (2:53 to be exact!)*YouTube video credit to JIGgameoverSAWA couple things to note:
1) A fully charged Plasma Pistol shot will down the Flood without killing him (you will know that the Flood is dead and won't come back if the game triggers a Checkpoint - if this happens, press start and restart the mission!) and
2) I crouched while pushing forward up against the wall as the Flood re-animated.
Watch the video several times and use the markings on the wall as a point of reference for where the Flood should go down and where you should position yourself. I can't stress this enough, the positioning of both the Flood and your position on him are crucial (again, use the markings on the wall as a point of reference of where to position yourself!
The above video doesn't cover an entire playthrough of the level so to finish that off, please refer to the video below and fast forward to 2:15 (after the cut scene) for an effortless way to wrap up the mission!*YouTube video credit to Nak3d Eli