Dead Space: Extraction

You'll unlock the Central Plaza Challenge after completing Chapter 3 of the story mode. The top score is 252,010 so you need more than this to earn the trophy.

Refer to the tactic in Overtime Sheet for this challenge. You'll face a new enemy, a flying necromorph. You need to be aware that they will swoop at you so be sure to be spamming so your rock saw stops them from damaging you. At the same time press to fire your flame-thrower and you'll set them alight so they burn as they fly around. I managed to get an 82 kill streak and ended the challenge with 277,631 on my first attempt so this is very easy. If you take damage in the first 6 waves restart or you won't have enough of a streak to get the required points.