Classes: Any combination of Tanks, Weapon Specialists, and Healers, but I recommend having at least one Tank for his living flair ability vs Mammoths and at least one Healer (though two is preferred). I don't recommend having more than one player play as an engineer if people are going for 'escape with all 4 classes'.
You can actually have someone quit out at the end when you're protecting the four monitors, activate two easy relics, switch classes to engineer, and rejoin to get the 2-relic achievement as well as credit for escaping as an engineer without having to play the entire match as that class. Just do it after the last 3 obelisks when the bridge opens, but before you initiate the last fight, so that they can take their time getting a little money from the players that stay to go buy a new gun.
It is HIGHLY recommended to have at least two people, one tank and one healer, with their class-specific 15-tooth ability just in case you get into trouble. This likely will be on the first two Mammoths before your group has had a chance to get pumped up, or if you get a rough challenge near the end.
Loadouts: At least one guy running Feral Instincts, One Running Team Booster, and two running armor (one main and one backup). Surprisingly IMS is good if you have the new upgrades for it, especially if you get an 'inside the circle' challenge and for the final area where you protect the 4 monitor things.
Everyone should run the same ammo type, preferably Incendiary if you have the perk to increase its burn length (damage). Everyone should also have Riot Shields. Sentry guns are ok just be careful with them and pick them up until you see the challenge if they're out at the start of an obelisk so you can put them in a corner if need be.
One guy is main shields and should get it to at least level 4. Backup shields guy should take his to at least 3, but preferably 4. Same for the main ammo guy and backup ammo guy, though with all 4 players running ammo and no one putting points into pistols, everyone should be able to drop ammo if needed in the heat of battle.
Everyone should max their class skill eventually unless you have 2 healers, in which case healer 2 should only go to level 4. No one should put anything into pistols save for one point for the increased movement speed with a pistol out.
Now for reference sake, there are 3 weapon schematic spawns. They will NOT always have schematics, but these are the 3 locations they can be at. Generally two of the three will have schematics, but the schematics are totally random.
Number One is to your immediate left as you exit the tunnel at the start if you hug the zone wall. Facing out from that one, #2 is straight across the ravine as you round the first bend in the trail when LEAVING #1. Number three is pretty far from the exit tunnel, but if you exit the tunnel and turn to your right instead of left and hug the zone wall, you will run into it.
Spawns 2 and 3 ALWAYS spawn a Mammoth.
1. Low Ground - Simply kill enemies that are higher than you. The exact range is hard to determine, but I've killed enemies on a ledge not far above me and they counted. Flying enemies count too. You will be killing loads of flying enemies as several challenges call for them.
2. Kill 5 bombers before they explode. - Simple enough. The only real problem comes when the game just doesn't SPAWN them. We failed one run on the 2nd to last hive because only 3 spawned. And we were watching VERY closely so we know only 3 spawned. Bombers are the glowing yellow buggers that come down from the sky, like flying seekers basically.
3. Kill 'X' Flying enemies. - Just kill Gargoyles and/or Bombers for this one, rather simple.
4. High ground - Similar to low ground but slightly trickier as the enemies don't tend to stay below you long. This is where flares come in handy. Just toss a flare down below you from a ledge and go to town.
5. Kill X enemies with a marked weapon. - Basically the same as weapon kill challenges but instead of being a weapon type, the game will pick 2 (maybe more?) specific weapons and highlight them with an orange cryptid symbol. Buy one of these and go to town. It helps to know approximately 'where' the various weapons that you like/don't like are located so you can go to the better of the options here.
6. Kill a Gargoyle with a melee attack. - Self explantory but a tip is to put some rounds into a gargoyle (you get a feel for how much it takes to kill one, so take it to roughly 50% health), then hide inside a cave/under an overhang. This will cause it to land and come walking over to try and get you, at which point everyone can start knifing it. It's actually a pretty easy challenge if done right. Thanks to GamerChik for reminding me to put this in.
7. Have every player buy a (different?) gun. - Simple, easy. Just have everyone run and buy a cheap but decent gun right away. Thanks to xI XboxOne Ix for reminding me of this other new one.
We also still have the old (hated) standby challenges like weapon-type kill challenges, accuracy challenges, killing enemies everyone has damaged, and killing marked enemies. These follow the same strategies as previous completionist runs. I was going to list all the weapon locations and their types here, but given the cryptid symbol waypoints now it isn't necessary. Just look for the cryptid symbol for weapon challenges. And pray that you don't get the 50% accuracy challenge on the very last obelisk like I did once on a solo run. Ug!
For an easier run: At the very beginning, exit the tunnel and head left to schematic spawn location #1. Kill the Rhino or Scorpions and look around. If there is an Ark here have one person buy a good weapon as soon as possible and grab it. If there is a Venom schematic here you're in luck because you can get at least 2, if not 3 people a Venom weapon in the first area before you even open the door to area 2. One person can even build it before you do the very first obelisk. Your group can always keep quitting/restarting until the Venom schematic is in this very first location to make the entire first area, including the two Mammoth spawns, easier, especially when you get the 'spend no money' or 'use no abilities' challenges.
If there's a gargoyle out, just ignore it and hide under a ledge/mushroom/etc near the Obelisk and deal with the smaller enemies. The gargoyles, when they're high up, will likely waste your ammo and maybe even kill you or get you killed by smaller enemies. Eventually they'll come down and walk near you allowing for an easier kill. Or deal with them after an Obelisk is done and the other enemies are dead. Of course if it's a challenge for flying enemies this changes things. Just have 2 guys focus on the Gargoyle and two focus on keeping smaller enemies under control.
Also, you can farm infinite enemies at the end of areas 1 and 2 where you use the predator to destroy the obelisks. It's not a bad idea to have everyone max out their money before moving on to areas 2 and 3. You don't really need it, but if you're struggling it might help.
Lastly, the new perk that prevents you from getting snared by hunters and seekers is a godsend on this map. There are TONS of hunters. The mammoths spawn the crap out of them if you don't kill the mammoth fast.