Miasma Chronicles

This achievement isn't as tough as it sounds. I strongly recommend that you play through the campaign at least once on a lower difficulty beforehand so you know what to expect and pick up information about different abilities, perks and so on. It really helps so you know when the ambush battles occur so you can prepare beforehand (most battles occur when you instigate them, but the ambushes are triggered by story events and throw you straight in so you can't thin out the enemies by picking off a few beforehand).

A few pointers:

(1) Use stealth as much as possible - there are only two stealth weapons - Jade's default sniper rifle; and the Mute assault rifle which is picked up at the very start of Undertown (it's on a linear path at the very beginning). You reach the Undertown area after you enter the Mines (which happens after you fight the Frog boss as part of the main story). Pick off whatever enemies you can stealthily to thin the herd.

(2) Save-scumming is still possible but is limited. The auto-save that occurs in battles happens (a) when a battle starts (oth if you instigate it yourself, or if you are spotted); and (2) at the start of each round. So if you miss a key shot, you can reload and it will take you back to the beginning of the round (auto-save doesn't occur after EVERY character's move).

(3) Use glass bottles to lure enemies away from groups so you can pick them off.

(4) Save your Rage shots for stronger enemies wherever possible, even when you're stealthily picking enemies off. Sometimes you have to waste a Rage shot on a weaker enemy, but where possible, try to juggle targets so that Rage shots are used on stronger enemies.

(5) Get into the habit of changing weapon mods and respeccing your perks depending on the fight and situation. It doesn't cost money to respec your perks. For example for Jade it helps to respec the perks which increase her Critical Chance stats - one of them gives an increase if she is on higher ground to the enemy; and another which gives an increase on unharmed enemies with full health. Just before story-related ambush fights you can remove perks which increase Critical Chance from Ambush perks/weapon mods as you're obviously not able to ambush the emeny in these situations. Yes it's alot of micro-management, but it pays off in the early-mid game as you're obviously not fully levelled up and won't have enough upgrade points.

(6) Buy the EDZ Col Rifle for 7000 plastic when you reach Club 14/Breakfast Club. It's insanely powerful and has strong Crit stats. I recommend giving it to Jade and upgrading her Berserker perk. If she gets a Critical Kill she gets an Action Point back and can basically chain kills together as long as she has ammo.

(7) Stock up on and make use of grenades and other consumables. In the first half of the game you don't need to use them much, but certain grenades like the Acid and EMP ones are limited in number so it helps to stock on a few. Acid Grenades ones are great for AOE, damaging humans and robots over time, and most importantly they will chip away at their Armour. This is especially important later on as your Ability cooldowns don't reset inbetween battles like on lower difficulties, so you won't always have access to abilities which reduce enemy armour. Remember that Miasma enemies are immune to acid effects, but Fire works fine (similarly Robots are immune to fire, but acid works fine).

(8) Remember that using a Miasma ability or a consumable does not end your turn on your first Action Point (whereas shooting your weapon does). So you can use your first Action Point to use a consumable, and then fire your gun using your second.

(9) In the late-game (especially the final battle) it helps to equip and use the Teleport Miasma ability on enemies. This allows you to teleport them next to each other so you can use a single grenade on them e.g.: you can use a single EMP and a single Acid Grenade to disable and damage multiple enemies. It helps you to save grenades as some are limited in number.

(10) Shotguns are decent as they fire within an AOE cone. I like to upgrade it with a scope increasing it's range so I can hit more things, and the more you hit, the more damage you can do. Diggs is great for this as he has the run-and-gun perk and makes it easier to flank enemies, and he is tanky as he has armour and health perks.