don't even bother with the infections if you are on easy or normal... keep your attention on the combat forms, shoot the carriers as soon as you see them, and DON'T use plasma greneades! they could get stuck to a jumping combat form and blow you up too... keep the shogun an AR is you are on easy or normal, but anything higher, ditch the AR... even a human pistol is beter because 2 shots anywhere on any form of flood WILL kill them, whereas the AR takes up to half a clip... back up while fighting thm, keeping them spread thin, and toggle between your weaopns... if you shoot a carrier directly in front of you, run backwards and jump at the same time to gain the best distance from them... reload as often as possible, especially the shotgun... some of the human combat forms will have a rocket launcher... kill them quickly, but leave the launcher behind, as its no use to you... when you reach one of the 10 sets of security doors, watch the hole up top as it first opens, as sometimes (especially at the end) combat forms will sail through them... Skeet shooting anyone?
each time you get off an elevator, be ware that there are going to be dozens of carriers dropping down around you endlessly... on a lot of points, the flood will respawn endlessly keeping you pinned down, unless you keep traveling past the spawn point... if your shields drop, run... a single infection can take you down without your shield... make sure you don't get surrounded, and be aware that the longer it takes you to move through the level, the greater the chances that you'll run out of ammo, die, or encounter much worse odds in the ending of the level, which is hell by itself...
