The Evil Within

For this achievement you must play the entire game without using any Green Gel (Apart from in the tutorial section). This will also allow you to New Game+ with tonnes of green gel if you still collect it (I had 350,000+ at the end) which will make getting more achievements later much faster.

You Cannot do this on New Game+

NOTE: On New Game+ you will only be able to select Casual.

For this achievement I picked Casual. This is a no brainer as enemies will still be tricky due to the fact you'll essentially never be able to upgrade your damage, stock or weapons.

Try to pace your ammo between your guns. As a rule you'll only be able to carry a maximum of the following (including the loaded mag):

16 Pistol Rounds
8 Shotgun Shells
2-3 of each Crossbow Bolt
3 grenades
10 Sniper Rounds
12 Magnum Rounds
2 Medkits

I'd suggest working toward the collectibles in the game mainly for the safe keys. These keys will allow you to re-supply ammo and medkits from the safe's you open each time you return to the hospital ward.

You are able to use the Super Medkits, which can be useful to keep for a while unti you need health. This will allow you to heal all damage you have in a pinch.

I wouldn't suggest that most people get a lot of the miscellaneous fighting achievements such as 'Bathed in Flames'. The demon creature known as 'Laura' takes too much of your precious ammo and resources that it may be worth missing until another playthrough. However I myself managed to kill all enemies in the game whilst doing this except the Dog creature 'Sentinel'; so it is possible for the most part.

If you find yourself using too much of an item or not using the best of local environments resources effectively don't be shy with reloading checkpoints. I found it was sometimes worth checking an area after a fight to see what ammo was available to re-stock in order to make later parts easier.

A good technique to kill basic enemies is melee attacks. I'd suggest if you're one-on-one with an enemy to hit him/her once at a time, retreating from their counter and repeating. This saves on ammo and just takes some practice/time.

If you can sneak past/stealth kill an enemy, do it. If you know the enemy can be left alone rather than engaged then always try to evade them.

If you find hatchets or torches, use them! These will insta-kill all smaller enemies.

Don't be too stingy with matches. If you see a group of enemies shoot their legs with a shotgun round and burn the group to save on ammo.

If you see bottles, throw them into enemies' faces and stealth kill them to save ammo.

Stock up a lot of trap parts. If you're fighting a particular boss that's causing you trouble make explosive arrows to help you out. Incendiary arrows are also useful when facing laura, but be warned they cost 5 parts a piece.

Hope this helps guys!