Notes for par scores on all levels:
Par scores are heavily influenced by par time.
Note: Competitive Score shows the time multiplier bonus; Regular Score does not. The time multiplier bonus still exists in Regular Score, it only shows up at the end of the mission. With Regular Score, you may not see the time bonus, especially on longer missions (credit: EaseAndInspire)
During "par time" all scoring is tripled.
After "par time", you have 10 minutes where your multiplier goes from 3.00x down to 1.00x. For example, if you kill an elite for a pop up of "+200", the score will show 600 during par time, but then will trickle back down to 200 when the multiplier goes down to 1.00x (and will be 400 if the multiplier is at 2.00x).
After the "ten minute down to 1.00x" period, one of two things happen:
1. You get a 2nd grace period, of about 10 more minutes. Multiplier is already at 1.00x so nothing else happens with it.
2. All positive scoring is done. All kills show up as red "0", but you will still lose points for dying, team kills, or checkpoint resets.
After that (Par time + 10-minutes + possible grace period), all positive scoring is done no matter what. Negative scoring is still active.
If you've already achieved the par score, you'll still have to beat the level while making sure you don't have enough negative scoring (deaths) to go below it.
For this specific mission:
Level: New Alexandria
Par Time: 20:00 minutes
Par Score: 22,500
Skulls: Catch, Famine, Fog, Thunderstorm, Tilt, and Cowbell (non-scoring but accelerates explosions)
This one I got accidentally...
At a certain point you're told to escort another UNSC ship. You'll get a yellow defend symbol.
If instead you stay away from it, banshee teams keep spawning. You'll have plenty of time to keep killing banshees. Once you've hit 70,000 points during par time (with 3.00x multiplier) you'll be at the par score (it's 23,333 points at 1.00x).
I didn't realize that the banshees kept spawning and you needed to fly over right by the ship to escort it!
I would recommend getting 80,000 or 90,000 points just to be safe.
If you're stuck on the part with the hunters, just remember that you don't really need to kill them - just press X on the jammer at the back of the club and escape. Good luck!