Edit: 343 decided the achievements were too hard so they decreased all par scores based on peoples performances on the missions, and laughed at everyone including myself getting par scores of 25k + (half Halo 1, ALL Halo 2). If you haven't done any yet, congrats you get it much easier then the first people to attempt par scores. For this mission, you need 14,000 instead of 25,000, follow my method below and instead of normal you can probably do this one on easy...
To obtain this achievement you need to achieve a par score of 25,000 points. My method is for normal mode, doing this method I did it in 11:44 and got 26,964 and this was running as fast as possible skipping enemies im sure, but I know I killed most.
Skulls: Catch, Famine, Fog, Jacked, Streaking (have overshield basically whole run), Thats Just... Wrong
I probably could have gotten away with having Thunderstorm on too but it was unneeded at the end. If you die, just restart the level, its short anyways so don't worry too much if you get stuck by a grenade, doing the save and quit method would prevent the achievement.
The whole level you are going to want to use the BR headshotting grunts and elites, with a plasma pistol to take the elites shields out, and don't forget to throw grenades.. A lot. Once I got to the armory you can take the shotgun from the dead body after killing the 2 elites. I ran through the rest of the level with the shotgun and BR, Shotgunning elites and headshotting grunts with the BR.
When you get to the end make sure to kill the grunts immediately and head left then kill the elites 1 at a time or what ever works with your shotgun. Easiest level for Halo 2 par scores in my opinion, if you look through my Par score achievements backwards to do the hardest ones first.
Any questions or comments feel free to message me or comment on the solution, good luck and have fun!