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: Nightfall
Par Time: 10:00 minutes
Par Score: 7,500
Difficulty: Heroic
Skulls: Catch, Famine, Fog, Thunderstorm, Tilt, and Cowbell (non-scoring but accelerates explosions)
Since this level is so short on par time (10-minute par time), you'll have to run through a chunk of it.
Kill the first elite as instructed and then hug the right wall.
Keep using your armor ability (sprint) to until you come right into a 2nd floor building. Jump onto the 2nd floor and curve all around to another building behind it. Enter that building.
Go up stairs and once again hug the right side.
You'll finally be spotted by enemies. You'll have to about 5 grunts to kill - try tossing a grenade. Go up the stairs again and you'll come out by a turret. Jump down past it and you'll see some red flares ahead of you.
Keep sprinting towards them. Ignore the huge enemy beasts and keep sprinting towards the green flares. When you come out to the Militia, hug the left side. Sprinting and jumping at the same time allows you jump the wall (end of the bridge). Go forward and you'll see more green flares. This is the riverbed the militia would tell you about after saving them.
Keep sprinting and then finally you see the "I'll just leave this here" pop up at the bottom. You should be at about 4 minutes total time.
Now you have to kill everyone in the last two sections.
You won't beat the par time, but 7,500 isn't that hard of a score with the above skulls active, and you'll have about 25 minutes to get it!
The skulls make sure that there are plenty of plasma grenades, although you do have to avoid getting stuck. The rank upgrade isn't as bad as it sounds - it's not like all silver elites are upgraded to gold. Good luck!