Dead Space: Extraction

You'll unlock the Extraction Site Challenge after completing Chapter 2 of the story mode. The top score is 251,010 so you need more than this to earn the trophy.

You get 250 points for each limb you take off, 100 for each item you pick up and 20 for each perfect reload. You then also get points on a sliding scale based on how many enemies in a row you kill without taking damage, starting on 500. So if you kill 2 enemies without taking damage you get 500 for the first and 550 for the second. If you build this streak up to 20 you'd get 1,450 points for the 20th, 1,500 for the 21st and so on. I managed to get a 91 kill streak (there are only 91 enemies) and ended the challenge with 289,238 points. If you take damage in the first 6 waves restart or you won't have enough of a streak to get the required points.

I have found an incredibly easy way to get through some of these challenges. The flame-thrower. You can't unlock this until Chapter 3 in the main story and you'll not be able to fully upgrade it until the end of Chapter 8. Now if you are using a DS3 (recommended for challenges), what you need to do is constantly spam so you are using your rock saw. This acts as a sort of shield against necromorphs. While doing this you also want to gently tap while having the flame-thrower as your weapon (be sure to select it as the starting weapon before you begin each challenge). This will give off jets of fire which will set light to the necromorphs. You won't be able to get full points for dismembering limbs, you'll get a flat rate of 500 per kill + the sliding scale multiplier. This is more than enough to reach the score targets however.

The benefit of doing this is that you start with around 300 shots of flame which easily lasts until round 5-6. You also get 100 shots for every pick-up so be sure to check out crates and of course the floor after killing necromorphs. All you need to do is set fire to the necromorph and let them burn for easy points. When a necromorph is set alight it also staggers backwards a bit so you don't need to panic if they seem like they are about to hit you. It's an incredibly easy way to take out 3-4 at once when a normal gun would leave you getting swamped and more importantly, taking damage which kills the streak. Just remember, gentle bursts and not keeping your finger on the trigger or you'll be out of shots in no time. If you do find yourself out of shots then switch to one of the weapons you randomly got during the challenge and make full use of it until you get more ammo for the flame-thrower.