*Your HUD is only visible when you hit the M key.
*Enemies can kill you in three or so hits. However, you can do the same with nearly every enemy, *depending on the weapon you're using. The only exception to the “you can kill everything in three or so shots” rule is the Amoeba spawner enemy in D6.
*Ammo pickups will give you barely any ammo. This applies to regular ammo and Military-Grade Rounds.
*Gas mask filters found on the ground won't give you a lot of spare air.

Buy as many gas mask filters as you can before leaving Market station. Gas mask filters you pick up off of the ground will have less air in them than other difficulties, making it harder to survive when you filter time gets low. By packing as many filters as possible, you'll be saving yourself a lot of trouble and grief down the line. If you've found all of the money in the first three stations, you can easily get 40 minutes of air before you reach Dead City. If you quickly go through the levels where you need to use your gas mask and use the trick described in the next section, you can easily get up to D6 without having to pick up a new filter off the ground.

A good way to preserve air for your gas mask is to take your mask off. When you start hearing your character's gasps get raspy, put it back on. Then, after having it on for a few seconds, take it back off. Repeat. The time you don't have your mask on will add up, saving you a lot of air for when you really need it.

The exception to this is combat. Having to put your mask on in the middle of combat can cost you your life, so just keep it on until everyone is dead.

Ammo is scarce in Ranger Hardcore, so use the Knife to take down one or two weak mutants attacking you. It may be a little frustrating using the knife at first, but after some practice, you'll be able to slice 'n dice anything up to a Demon or Librarian with ease. The ammo you save will make humans, large mutant hordes and strong mutants much more manageable.

Stealth is by far the most effective way to take down humans. Enemies can kill you in about three shots, so trying to take enemies on head-first is suicide. Instead, either avoid them or silently take them down with Throwing Knifes and the Helsing when they're not looking where you are. It may be frustrating trying to work around the wonky stealth mechanics, but having to restart from the last checkpoint because an enemy alerted his pals is a lot less frustrating than getting killed by a stray enemy after nearly finishing a 10-minute gun battle.

Get the Stealth Armor when you're in Armory. Not only does it make stealth easier by quieting your footsteps when you walk, it also has night vision goggles, which will be handy throughout the rest of the game.

You might want to swap it with the Heavy Armor when you reach Polis, but the Military Grade Rounds spent purchasing it are better spent as ammo on enemies. Being able to take down enemies faster is much more useful than being able to take an extra hit.

Here's a quick breakdown of the best weapons to use in Ranger Hardcore.

The Throwing Knife will save your bread and butter before you get the Helsing. A single Throwing Knife will kill an enemy in one shot. That's nice, but what really makes it shine is that a Throwing Knife kill will take down an enemy without other enemies being alerted that you're here. Because of this, the Throwing Knife is essential for stealth early on.

Be careful when using the Throwing Knife. If a knife hits armor or even an ammo pouch, the knife will not kill your target in one hit. This will screw you over because the enemy dying after taking another Throwing Knife will scream, alerting other enemies to your presence.

The Helsing is your gun BFF when facing humans. Overpressued (represented by the pressure gauge on the gun's right being at maximum) shots not only kill human enemies in one shot, no matter where the arrow hits, they also kill enemies silently. This makes it the best weapon to use when sneaking around. If there's a pesky enemy you need to get rid of, just break out the Helsing, overpressure it, and shoot an arrow into his ass. He'll go down without making a noise, which would alert his pals.

When using the Helsing, always make sure that the gun is overpressured. If you're going into a new room, overpressure. Suddenly see someone you need to take down? Hide, overpressure, then shoot the jerk. If the gun isn't completely overpressured, the arrow might not kill the enemy in one shot. If it doesn't, you're screwed. The follow-up shot you'll have to take will make him scream, which will alert every enemy in the map that you're around.

The Helsing is also handy for certain stronger mutants later in the game. Overpressured shots will make quick work on Librarians, especially if you hit the head. Don't try it on packs of weaker enemies because the gun doesn't fire enough to take them down before they overwhelm you.

By the time you reach Spara (the church fortress you go to after leaving the Library), you might want to swap it with the Heavy Automatic Shotgun. The Helsing is too slow to quickly take down the large amount of mutants the game tosses at you on the way to D6, while a full magazine fired from being completely overpressured is needed to take down a single Amoeba Spawner.

The Revolver is very powerful in Ranger Hardcore mode. It will put down a weak mutant in one or two hits, while stronger ones will take three or four. This makes it great for quickly taking down pesky mutants and conserving 5.45mm ammo. If you're out of 5.45mm ammo, each round packs enough punch to take down most mutants quickly.

To get the most out of the Revolver, pick up one that has an extender barrel (not silencer) and a rifle stock. Those upgrades makes medium and long-range shooting much easier.

The VSK is a good supplement for the Helsing. Use it to destroy lamps without enemies noticing and to keep your position semi-hidden when you have to engage in firefights with enemies.

The AK-74 should be your automatic rifle of choice after going through Polis because you'll no longer need to use stealth. The AK-74 does the most amount of damage per bullet, which is very useful for keeping mutant hordes under control. The decent-sized magazine means you can do some damage before having to reload.

To really get the most out of the AK, use Military-Grade Rounds. A single bullet will put down any weak or medium-strength mutant in one shot, down the black Nosalies in about two to three shots and kill the Amoeba spawners with about half of a magazine. Since you can't buy anything after going through Polis, you might as well put your Military-Grade Rounds to use instead of letting them rot. However, try to burn through your dirty ammo reserves first so that you'll have enough Military-Grade Rounds to take down the Amoeba spawners in D6.

The Heavy Automatic Shotgun is THE anti-mutant weapon. The sheer amount of pellets this thing spews out means anything will die before you're used a full magazine. This makes it perfect for taking down any type of mutant, from a horde of Watchers (the hairy rat things you meet on the surface) to the Amoeba Spanwers you meet in D6.

The best time to pick up the Heavy Automatic Shotgun is in Sparta after leaving the Library. Since you no longer need to worry about stealth, replace your Helsing with the Heavy Automatic Shotgun so you can clear out the mutants the game tosses at you with ease when you're going to and in D6.

A good idea is to conserve shotgun shells as much as possible in the early and mid-game so that you'll have as many shells as possible to use when you leave the Library. The Heavy Automatic Shotgun eats shotgun shells like crazy, and you might not have enough money to purchase a lot of shells. By conserving shells as much as possible, you'll be able to have a ton of ammo by the time you leave the Library.

The end! If you have any more tips, let me know and I'll put them up.