Halo 3

You can get this by skill or by cheating a little.

If your good enough you can do it on your own - the only problem is that when you die, you go back to the last checkpoint every time - or if you have a second controller, load the map up and have that controller stay back in case you need to respawn - if you both die then yes, you go back to the last checkpoint but if one dies then the other has a chance to respawn. It is up to you whether a friend takes control of player 2 or whether you just leave them idle.

If you do load up a second controller with a human playing, try not to let them take all your kills - only let them get the odd few to help you advance. Killing larger vehicles and enemies such as scarabs really boost your score and you'll find yourself getting 20/30 thousand quite quickly.

My setup was as follows in terms of multipliers and skulls:

Normal Difficulty
Free For All (Especially if more than one player)
Catch Skulls (Every NPC carries two grenades and throws them often)
Thunderstorm Skulls (Upgrades enemies to their stronger versions.)
Fog Skulls (Your motion sensor disappears)

Doing it inside the 2.00x time multiplier might help but with those skulls on and on normal I didn't find time to be an issue.

PLEASE NOTE: The achievement only counts for individual scores so if you are in a team and get over 50,000 points then it will NOT count unless you score over 50,000 individually.

Either do the above solution with a second controller. Or do it the way I did this, I went through the mission with one other person on Heroic with Fog, Thunderstorm, Tough Luck and Famine enabled.

I thought I would put out there what worked for me for both of the 50,000 score meta game achievements (The Ark and The Covenant). Bear in mind, this method is quite slow and grindy. However, time and deaths aren't really a factor and you should clear 60,000 -70,000 points with no problem.

SKULLS: Tough Luck, Fog, Thunderstorm, and Mythic. These skulls give you a 6x scoring multiplier and are plenty for what you need. I added Cowbell, Grunt Birthday Party, and IWHBYD for fun.

DIFFICULTY: Normal. The above skulls will give the game a feel closer to Heroic difficulty. You'll die here and there but the penalty will not really hurt your score.

As I said, don't worry about rushing through the missions. They are very long and you probably wouldn't have gotten much of a time bonus anyway. Your goal is to kill/destroy everything. Headshots, multikills, and most of all enemy vehicles and turrets. Use a vehicle with firepower whenever you can. There is nothing wrong with grabbing a ghost and spamming it's gun at a wraith across the map. When in your Hornet, spam those rockets and clean up every Banshee in the air and AA gun on the ground from a distance. Also, when driving a Warthog remember that you get credit for your gunner's kills! Most important of all is to note that in either of these big missions you will get a Scorpion Tank to use. In the Ark mission this is clear but for the Covenant mission you could miss it if you rush. Right after clearing the third tower and getting ready to head to the double Scarab battle, there is a Warthog sitting out for you to take. Don't do it! Wait a few seconds and the UNSC will drop in a Scorpion too! Any opportunity to use a Tank, you take. Period.

Don't worry if you don't seem to have enough points and you're deep into the mission. Both The Ark and The Covenant and heavily backloaded points wise. I was down 10,000 to 15,000 points going into Rally Point Bravo for each mission and easily hit 70,000 points for each mission in the end. Good luck!

For this achievement you'll need to earn at least 50,000 scoring points on the sixth mission of the Campaign, The Ark. This can be done solo or with a few buddies. (I got all mine solo and using the method below)

First you'll need to enable either Free-For-All or cooperative scoring from the campaign options. Then select the following for quickest results:

Normal Difficulty
Catch Skull - (1.00 multiplier)
Fog Skull - (1.00 Multiplier)
Famine Skull - (1.00 Multiplier)

So you'll be playing on Normal difficulty with enemies chucking nades alot, no Mini-Map, and ammo pick-ups are scarce. However, being on Normal difficulty will make this a cakewalk. And having these 3 skulls on will start your kill scoring at a x3 Multiplier, so as long as you finish the mission within a reasonable time, and die little-to-no times you'll have more than enough points to pop your achievement!