The Flood Halo 3

When killing the Flood when you reach the Flood Planet, it is best to concentrate on your radar in the crowded areas and just on your radar. It's important to pick up weapons with a lot of ammo whenever you can because you'll be using up all your ammo on killing at least one or two floods. Where you come to spots that aren't so crowded, it's best to let the floods come to you, so you can get a good target and shoot them easily one at a time. I learned the hard way that you will want to make sure the body is completely destroyed even after it falls, otherwise the floodlings will resurrect the body and you'll have more trouble. There are two body types however, that you will not be able to completely obliterate, and those are the spider flood and the massive floods that turn into the spider floods. You'll figure it out, I can't be clear enough only because there is no specific names for each flood body that I know of.

However, in crowded areas of flood, you must use your radar and look at the the whole time if you can while using melee or gunfire. The best weapons I know of using against the flood is the Energy Sword, and the Flame Thrower. The great thing about the Flame Thrower is that if you figure out a way to get all the flood lined up to "Get Some" you can burn one flood and block the whole passage between you and the flood by torching the ground in front of you and therefore torching some of the flood which then incidently other floods will pass through or touch slightly the burning flood, resulting in a lot more burning floods. Also, for the jumping floods, or any flood that dares jump on you for that matter, there is the Energy Sword, which I promise will be a great friend when you need it most. However, be frugal about your hits, and try to get them the first time. When using the Energy Sword, you usually only have to hit them once, and they automatically burst into pieces for you. Same goes with the Flame Thrower, you just have to hit the trigger once, and quickly, then they'll burst into pieces once they're done being toasted.

Then of course, you have your very annoying bug floods(the spider floods you can't burst into pieces) that attatch themselves to the wall and shoot yellow spikes at you and can turn into a crawling spider or turn into those huge big floods. Worry about those last. Just try to stay out of line of their fire. You should be good if you can get onto a high ledge or something so you're not on the ground where you can get mauled over and shot at. Just make sure you can get cover on top of the ledge before you torch some floods.

Once you got the walking floods taken care of, charge into the firing zone with your torch, lighting one, then retreating into your 'safe spot' until your shields go back up. Then repeat the method.