Dark Void

This achievement isnt too bad if you have played through the game already. Playing it through without any modifiers only results in around 750-800k so turn one of them on. I chose Legend cause the AI assistant doesnt really do anything for you.
My weapon choices were Liberator assault rifle and the Reclaimer sniper rifle. I only used the sniper for the most part unless ran out of ammo. Will have plenty of points more then you need so upgrade whatever 2 weapons you use both to lvl 3.
At alpha site i pretty much just flew straight up into the air and sniped a lot of the enemies as they spawned and dropped down for ammo pack when needed, but without any health or difficulty modifiers you can also just run around melee killing stuff mostly here. (Just watch out for the red guys, they explode once in melee range).
At bravo site I just stood on the little platform canopy directly over an ammo box and sniped everything. Empty ammo, drop down, reload, jet back up on top and repeat. This was the easiest imo.
At delta I would just go right into the center to start. At the beginning you get hit a bit cause theres jet pack enemies to start but once they are down the mobs pretty much come from only 3 sides and 2 of them are the tunnels on either side of you so they are funneled right into your sniper sites.
For the Flying Knights that show up I used inside the cave at bravo and inside a tunnel side at delta to take them out easily. At alpha site I didnt use an indoor area, just stayed on outer edge in cover since it hovers over the site directly. When theres 2 at alpha is when its tricky but focus on one and if you have to jet pack away. They are accurate but locate target slowly when you move.
By end of wave 5 you should have both weapons upgraded fully to level 3, 75,000+ points and a multiplier of 50+ (mine was 87,475 multiplier 73)
wave 6 is when i got first flying knight but its all alone so should be no trouble
End of wave 8 I had 500,450 with 102 multiplier
At wave 10 you end with 2 flying knights at the same time. Again if you can be in a cave or tunnel do so, makes life much easier. I finished with over 100 multiplier and 816,400 points. With the Legend multiplier turned on from the start thats x2 points so Plink.....achievement! 1,632,800 points, plenty to spare. If you like to use guns on your jet pack as well, you have enough points to upgrade that as well as long as you keep your multiplier up high.

Please feel free to leave any comments and goodluck with the achievements!