What the best mission(s) to get 20,000 or more points since the recent update? I dunno if someone else posted this or not I was just curious. I also had progressed in this challenge by two missions but since two firefight related challenges didn’t give me their rewards I had to do a hard reset so I’m back at zero. Sorry that I veered off topic slightly but I’d thought I’d mention that little detail.
What the best mission(s) to get 20,000 or more points since the recent update? I dunno if someone else posted this or not I was just curious. I also had progressed in this challenge by two missions but since two firefight related challenges didn’t give me their rewards I had to do a hard reset so I’m back at zero. Sorry that I veered off topic slightly but I’d thought I’d mention that little detail.
Halo 4 with some skulls (2 or 3) or just play on legendary but under par time.

I did the first mission in Heroic with 2 skulls and I got like 40K.

On legendary with 4 skulls I got like 90K in the first mission.
Pretty much any level on legendary without any skulls will get you well over 20k points, unless you're skipping lots of enemies and just running through the mission
There are some suggestions in this Twenty Grand Challenge thread.

From my experience, Floodgate seems to be the fastest.
It takes some time, but New Alexandria worked really well for me. Just farm banshee's.
One of the best methods I found was to start halo 4 Shutdown, heroic or legendary with your choice of skulls up to around 4x + score, grab the pelican, destroy all the phantoms outside the first two towers, then fly to the final back tower and perform the easy as pie level skip and then run through the last quarter of the level.
Dawn on Halo 4 on Legendary should get you 20k. If you know the level, you don't even need to use any tricks to get under par time. Add in a couple skulls if you're worried about coming in under 20k.
the package on reach heoric no skulls
Honestly, I was smashing the 50,000 on kizingo boulevard Heroic, no skulls. It was pretty easy to do, now it will be a breeze with the reduction of points. I was getting 65,000+ on that mission.
Any mission with a lot of vehicle action should be good, those missions in Halo 3 and Reach can go above 100 000 points easily with the highest score multiplier to give an idea.

The Storm isn't very long, with the 3 major sections being fairly close to each other.

The Package is Reach is easy even on LASO, the part at the glacier is only a bit harder but the score should be above 20 000 long before the courtyard of sword base, all skulls is probably too much. Not required but an ODST with a Focus Rifle is a decent laser guide for the tank, it's like the handheld weapon with the highest attack range given to a NPC.