Alright start 343 guilty spark on co-op(note- it doesnt work on 1 player) so while your still in the pelican keep pressing the grenade button untill you run out and.. WALA! ur still in it and it will take off with you in it! anyway, it will land near the edge of the map, now get out (note- make sure that a player stays with the crashed pelican so u can spawn with him) and go the way that the pelican is facing and then jump on the entry to the building u would usually go thru on the mission then drop down and quickly look inside the entrance and u will just see 3 floating assault rifles just shooting but there is no marines holding them. now here is another glitch spawn with the other player and continue going around the edge of the map untill u find a lone marine, just standing there not moving and he has no gun (note- if u hit once he will die). and if u wait a long
time at the pelican and then go out looking again u will find some flood bodies which is weird coz u dont meet the flood yet but we have.