If playing on a difficulty higher than easy and moving faster horizontally than half of your jump height when you land, then you make a sound that is multiplied by the difficulty. Higher is more sound.
else if ( (Level.Game != None) && (Level.Game.Difficulty > 1) && (Velocity.Z > 0.5 * JumpZ) )
MakeNoise(0.1 * Level.Game.Difficulty)

If jumping you the amount of sound you make is influenced by the difficulty.

Damage taken is multiplied by the difficulty and always at least 1.

If playing on a difficulty higher than easy and moving faster horizontally than half of your jump height when you land, then you make a sound that is multiplied by the difficulty. Higher is more sound.
else if ( (Level.Game != None) && (Level.Game.Difficulty > 1) && (Velocity.Z > 0.5 * JumpZ) )
MakeNoise(0.1 * Level.Game.Difficulty * runSilentValue)

If jumping you the amount of sound you make is influenced by the difficulty.

Damage taken is multiplied by the difficulty and always at least 1.

In Biomod & Shifter, in unrealistic, dodging is allowed. I have no idea what this means but it's allowed.

Distance the AI checks for the player (2500) is dependent on and multiplied by the difficulty.
2500((1.00+(2.00*√difficulty))/3.00)

Distance the AI can see might (the code says 'probably does nothing') be dependent on and multiplied by the difficulty. I was unable to find another instance of SightRadius so it might be completely useless.

How well the AI can hear is dependent on and divided by the difficulty. This is dependent on the NPC, some have better hearing than others. Lower is better hearing.
HearingThreshold /= √difficulty

How well the AI can see is dependent on and divided by the difficulty. This is dependent on the NPC, some have better sight than others. Lower is better sight. The base value is always at least 0.0005.
VisibilityThreshold = FMax(VisibilityThreshold, 0.000500);
VisibilityThreshold *= (1.50 / (0.50+√difficulty))


How fast the AI can react when surprised is dependent on and multiplied by the difficulty. Higher is faster reactions.
ReactionLevel += ((deltaSeconds/surpriseTime) * (1.00+(3.00*playerDiffRoot))/4.00)

The amount of time the AI spends standing and looking in one place is dependent on and divided by the difficulty. Lower is less time.
Sleep((FRand()*2.5+2.0) / playerDiffRoot)

The AI is able to use the GEP gun's tracking feature if playing on realistic. (As of patch 1.0.1.2)

The accuracy bonus the AI gets from standing (like the player) is lowered on easier difficulties. Lower is better.

The base accuracy bonus the AI gets is higher on harder difficulties. Lower is more accurate.

The AI is able to use the GEP gun's tracking feature if playing on realistic. (As of patch 1.0.1.2)

If playing on unrealistic mode then the AI has a 25% (I think) chance to get a crowbar or sword instead if they are carrying a combat knife.

It looks like if you are playing on unrealistic then animals can have items and weapons.
Items including:

• Soy Food
  
• Candybar
  
• Sodacan
  
• Medkit
  
• Zyme
  
• Cigarettes

In unrealistic mode, all enemies seem to get a random item, as long as they had one previously. If they had one before then they can get:

• GEP Gun - if they didn't have a powerful weapon before e.g. an assault gun/shotgun, a heavy weapon, or were a robot.
  
• Dragon ammo if they didn't have a weapon
  
• 20mm HE ammo
  
• WP rockets
  
• Pepper gun
  
• PS20
  
• Flare darts
  
• Throwing knives
  
• Flamethrower (if they didn't have a powerful weapon) otherwise:
  
• Prod
  
• Explosive 10mm ammo
  
• LAW (if they didn't have a powerful weapon)
  If they didn't have a weapon they have a chance of getting:
  
• Sawed off shotgun
  
• Pistol
  If they are a MiB or WiB they can also have:
  
• All weapon mods
  
• Aug upgrade canisters
  
• Poison knives
  
• WP grenades

If the difficulty is higher than or equal to hard then the AI is allowed to use alternate types of ammo.

If an NPC searches for and finds a weapon on the ground or on a body they will pick it up. In unrealistic mode, this apparently includes non-humans.

It sounds like maybe if you disable a robot you can steal its gun on unrealistic?

Uhh, pigeons turn into rats when they die in unrealistic mode, if they're not in water and their health is over -100.

Pistol ammo may be explosive on unrealistic mode for NPCs.

In Biomod & Shifter, in unrealistic, dodging is allowed. I have no idea what this means but it's allowed.

Accuracy divided by difficulty. Lower is more accurate.

Damage bonus multiplied by difficulty.

Accuracy divided by difficulty. Lower is more accurate.

Damage bonus multiplied by difficulty.

Aggressive Defensive Aug level changed by difficulty.

Biocells recharge different amounts depending on the difficulty

The time it takes for mines to detonate is dependent on demolitions skill level and difficulty. The time is never less than 0.25 seconds. These are some pretty tricky calculations so they might not be 100% right. All figures rounded.

The time it takes for mines to detonate is dependent on demolitions skill level and difficulty. The time is never less than 0.24 seconds. These are some pretty tricky calculations so they might not be 100% right. All figures rounded.

This terrorist at the doors of the statue doesn't appear on easy or normal.

This rebreather outside UNATCO only appears on easy.

The medkit in the room accessible from the vents doesn't appear on hard or realistic.

The LAM outside Gunther's cell doesn't appear on hard or realistic.

The crate with a clip modification in the bunker doesn't appear on hard or realistic.

This crate containing a multitool near the sniper doesn't appear on hard or realistic.

The medkit in the crate at Filben's dock doesn't appear on realistic.

The medkit in the crate at the doors of the statue doesn't appear on realistic.

The lockpick at the lasers to Gunther's cell doesn't appear on realistic.

The LAM at the lasers to Gunther's cell doesn't appear on realistic.

The crate containing a gas grenade above where the medbots used to be doesn't appear on realistic.

The multitool at the top of the ladder in the bunker doesn't appear on realistic.

The crate containing 30.06 ammo on Filben's dock doesn't appear on realistic.

The crate containing 10mm outside the bunker near the crates doesn't appear on realistic.

The prod charger in the secret hatch by the sniper doesn't appear on realistic.

The PS20 at the lasers to Gunther's cell doesn't appear on realistic.

The crate containing 10mm ammo at the starting dock doesn't appear on realistic.

One of the biocells in the vent of the closet doesn't appear on realistic.

The multitool on the bookshelf in the left room on level 1 doesn't appear on realistic.

The multitool on the shelf in the right room on level 1 doesn't appear on realistic.

This crate at the end of the dock containing a reload modification only appears on realistic.

This crate at the end of the dock containing an accuracy modification doesn't appear on realistic.

One of the terrorists outside Osgood and Sons with an assault rifle doesn't appear on easy.

The lockpick in the top room of the building by the basketball court doesn't appear on easy or normal.

The crate containing 10mm behind the soldiers that give you gas grenades doesn't appear on hard or realistic.

The LAM in the top room of the building by the basketball court doesn't appear on hard or realistic.

The crate containing 10mm ammo at the bus stop outside Osgood's doesn't appear on realistic.

The crate containing 7.62mm ammo on the table in the park doesn't appear on realistic.

The crate containing a biocell inside Osgood's doesn't appear on realistic.

The crate containing 30.06 ammo behind the soldiers that give gas grenades doesn't appear on realistic.

The 10mm in the top room of the building by the basketball court doesn't appear on realistic.

The 30.06 in the top room of the building by the basketball court doesn't appear on realistic.

The crate in the trailer containing 30.06 ammo outside Smuggler's secret entrance doesn't appear on realistic.

The LAM on the phone booth by the riot cops outside Smuggler's secret entrance doesn't appear on realistic.

One of the medkits in the doctor's office doesn't appear on realistic.

The medkit in Paul's bathroom doesn't appear on realistic.

The multitool in Paul's secret closet doesn't appear on realistic.

The lockpick in Paul's secret closet doesn't appear on realistic.

The crate containing a prod charger in Smuggler's closet doesn't appear on realistic.

The crate containing 7.63mm ammo in Smuggler's closet doesn't appear on realistic.

These two crates on the roof tops near the billboards containing 30.06 and 7.62mm ammo don't appear on easy or normal.

This medkit in a chest in the new hole on the rooftops doesn't appear on easy.

Some buckshot shells on the top floor of the generator build do not appear on hard or realistic.

A crate on the top floor of the generator building containing 10mm ammo does not appear on realistic.

A crate in the last room of the new area on this map containing buckshot shells does not appear on realistic.

The lockpick on the 2nd room on the first floor doesn't appear on realistic.

One of the medkit crates in the medical closet isn't there on realistic.

The crate containing a biocell in Alex's closet isn't there on realistic.

The biocell under the rockets near the bathroom does not appear on realistic.

The range mod in the train carriage doesn't appear on realistic.

The 10mm ammo upstairs on the bed near the snipers doesn't appear on realistic.

On easy this chair after the turrets doesn't appear, making the terrorist walk around.

The soda can beside the chair doesn't appear on easy, or realistic.

The robot in the same place doesn't appear on easy.

The sniper terrorist patrolling with the robot in the area with the flaming barrels doesn't appear on easy.

This archive box next to the secret closet only appears on realistic. To take up the space of the removed biocell.

The LAW in the secret cupboard doesn't appear on hard or realistic

The LAM in the secret cupboard doesn't appear on hard or realistic

The multitool hidden in the pipe after the security bot and sniper doesn't appear on hard or realistic.

The pistol in the secret cupboard doesn't appear on realistic.

The augmentation upgrade canister doesn't appear on realistic.

The biocell outside the other secret cupboard doesn't appear on realistic.

The medical crate containing a medkit in the second hidden cupboard doesn't appear on realistic.

The lockpick in the crate in the second hidden cupboard doesn't appear on realistic.

The crate containing 7.62mm ammo by the ambrosia doesn't appear on realistic.

The scope mod in the secret compartment doesn't appear on realistic.

The crate at the dock containing a multitool doesn't appear on realistic.

The 30.06 ammo in the secret compartment doesn't appear on realistic.

The multitool in the trunk in the barracks doesn't appear on realistic.

The multitool in Lebedev's room isn't there on realistic.

The biocell near the exit doesn't appear on realistic.

The crate outside Alex's room containing a lockpick doesn't appear on hard or realistic.

A crate by the basket ball court containing napalm only appears on easy.

The lockpick in Paul's secret closet doesn't appear on realistic.

The augmentation upgrade canister in Paul's secret closet doesn't appear on realistic.

The augmentation upgrade canister only appears in Paul's wardrobe on realistic.

The 30.06 ammo in Smuggler's hidden cupboard doesn't appear on realistic.

The security bot at the start doesn't appear on easy.

One of the soldiers by the robot doesn't appear on easy or normal.

The soldier on top of the 237615 building doesn't appear on easy.

The soldier in the center of the buildings doesn't appear on realistic.

He is instead replaced with one with a flamethrower on realistic.

One of the spiderbots in the sewer doesn't appear on easy or normal.

The other only appears on realistic.

Both cardboard boxes under the railway only appear on realistic to take over the space of the medical crate that isn't there.

One of the TNT crates in the hidden room doesn't appear on hard or realistic.

The medical crate containing a medkit under the railway doesn't appear on realistic.

One of the TNT crates under the NSF HQ doesn't appear on realistic.

The prod in the cabinet under the NSF HQ doesn't appear on realistic.

A crate under the NSF HQ containing a multitool doesn't appear on realistic.

A crate under the NSF HQ containing a lockpick doesn't appear on realistic.

A crate under the railway containing rockets doesn't appear on realistic.

A crate with a medkit in the secret room doesn't appear on realistic.

The UNATCO trooper at the start by the bus stop doesn't appear on realistic. Weird.

A crate under the railway containing ballistic armour doesn't appear on realistic.

The UNATCO trooper directly at the start of the map doesn't appear on easy.

One of the soldiers in the conference room doesn't appear on easy or normal.

The multitool in the room with the ladder doesn't appear on realistic.

One of the packets of 10mm ammo doesn't appear in Carter's armoury on realistic.

One of the clips of 7.62mm ammo in the armoury doesn't appear on realistic.

The range mod in the armoury doesn't appear on realistic.

The UNATCO soldier outside with the pistol doesn't appear on easy or normal.

The UNATCO soldier outside with the sniper rifle only appears on realistic.

The crate in the armoury containing LAMs doesn't appear on hard or realistic.

One of the crates in the armoury containing 7.62mm ammo doesn't appear on hard or realistic.

The multitool on the crates in the robot maintenance doesn't appear on hard or realistic.

The other multitool on the crates in the robot maintenance doesn't appear on hard or realistic.

The 3rd multitool in the robot maintenance (this time on the middle floor) doesn't appear on hard or realistic.

The crate containing a lockpick under the stairs of the command centre doesn't appear on hard or realistic.

One of the assault shotguns in the armoury doesn't appear on realistic.

Two of the assault guns in the armoury don't appear on realistic.

The flare darts in the armoury don't appear on realistic.

One of the packs of 10mm ammo in the armoury doesn't appear on realistic.

One of the packs of buckshot shells in the armoury doesn't appear on realistic.

One of the crates containing rockets under the stairs of the command centre doesn't appear on realistic.

The crate next to it containing buckshot shells also doesn't appear on realistic.

One of the assault rifles in the command centre doesn't appear on realistic.

One of the sawed off shotguns in the command centre doesn't appear on realistic.

One of the gas grenades in the command centre doesn't appear on realistic.

One of the MJ12 soldiers that attacks at the start doesn't appear on easy and normal.

One of the medkits in the bathroom lockers doesn't appear on realistic.

The multitools in the munitions bay don't appear on realistic.

The sabot rounds in the police station doesn't appear on realistic.

One of the 7.62mm clips in the police station doesn't appear on realistic.

One of the 7.62mm clips in the police garage doesn't appear on realistic.

The unobtainable augmentation upgrade canister doesn't appear on normal or hard, strangely.

One of the 7.62mm clips in the police office doesn't appear on realistic.

The other 7.62mm clip in the police office doesn't appear on hard or realistic.

One of the 30.06 clips in the police office doesn't appear on realistic.

The sabot rounds in the police office don't appear on realistic.

The augmentation upgrade canister under Max Chen's bridge doesn't appear on hard or realistic.

The 10mm ammo in the security office doesn't appear on hard or realistic.

The 10mm ammo in the secret painting doesn't appear on realistic.

The reload mod in the secret painting doesn't appear on realistic.

The assault gun in the new addition to the security area doesn't appear on realistic.

One of the boxes of shells in the new security area doesn't appear on realistic.

The 20mm HE ammo in the new security area doesn't appear on realistic.

The LAM in the new security area doesn't appear on realistic.

The crate containing a lockpick in the new area above the labs doesn't appear on realistic.

The multitool near the water tank doesn't appear on hard or realistic.

The crate behind the vans containing 10mm ammo doesn't appear on realistic.

The crate outside the Ton containing 10mm ammo doesn't appear on realistic.

One of the gas grenades in the building by the basket ball court doesn't appear on realistic.

The lockpick and multitool next to the subway don't appear on realistic.

The medkit behind Smuggler's mirror doesn't appear on realistic.

The crate containing a lockpick doesn't appear on realistic.

The crate containing 20mm HE ammo doesn't appear on hard or realistic.

One of the biocells in the Base Commander's building doesn't appear on realistic.

The medkit in the Base Commander's building doesn't appear on realistic.

The lockpick in the Base Commander's building doesn't appear on realistic.

One of the clips of 30.06 ammo in the crane doesn't appear on realistic.

The other clip of 30.06 ammo in the crane doesn't appear on hard or realistic.

The crate containing 10mm ammo in the armoury doesn't appear on hard or realistic.

The crate containing 20mm HE ammo in the armoury doesn't appear on realistic.

The crate containing sabot rounds in the armoury doesn't appear on hard or realistic.

The crate containing buckshot shells in the armoury doesn't appear on hard or realistic.

One of the crates containing sabot rounds in the other large storage building doesn't appear on realistic.

Both LAMs in the armoury don't appear on realistic.

The crate above the building in the armoury containing sabot rounds doesn't appear on realistic.

The crate above the building in the armour containing a LAW doesn't appear on realistic.

The crate containing a medkit in the trailer doesn't appear on realistic.

The 30.06 ammo in the trunk next to the door in the new building at the start doesn't appear on realistic.

The accuracy mod in the trunk next to the door in the new building at the start doesn't appear on realistic.

The 30.06 ammo by the dead Russian agent doesn't appear on realistic.

The two guards at the ladder at the front of the ship only appear on realistic.

One of the MJ12 guards at the dock protecting the ladder at the front of the ship doesn't appear on easy or normal.

Another one in the same place only appears on realistic.

There is a biocell under the dock where the ladder is on the floor of the water that only appears on realistic.

The GEP gun at the front of the ship doesn't appear on hard or realistic.

One of the multitools in the electronics lab of the ship doesn't appear on hard or realistic.

A crate containing a biocell on the dock by the ladder to the ship doesn't appear on hard o realistic.

A crate on the centre of the dock containing 10mm ammo doesn't appear on hard or realistic.

The assault rifle in the armoury of the ship doesn't appear on realistic.

A clip of 7.62mm ammo in the armoury of the ship doesn't appear on realistic.

The buckshot shells in the armoury of the ship don't appear on realistic.

The 10mm ammo in the armoury of the ship doesn't appear on realistic.

One of the biocells in the electronics lab on the ship doesn't appear on realistic.

Another multitool in the electronics lab of the ship doesn't appear on realistic.

One of the LAMs in the armoury of the ship doesn't appear on realistic.

A crate containing a medkit in the sickbay of the ship doesn't appear on realistic.

A crate on the dock by the ladder to the ship containing credits doesn't appear on realistic.

The biocell on the monitors of a new room accessible from the dock doesn't appear on realistic.

The soldier at the top of the stairs in the helipad doesn't appear on easy or hard.

A crate containing a multitool near the weld point on the right of the room that you enter doesn't appear on hard or realistic.

A crate containing a lockpick outside the room with the bilge pumps doesn't appear on hard or realistic.

A crate containing a 66% chance of a lockpick and a 33% chance for a multitool in the bilge pumps room doesn't appear on hard or realistic.

A crate in the helipad room containing a medkit doesn't appear on hard or realistic.

I really don't know how to describe this place. From the start of the level go right, go into the corridor and down the ramp. Go right and go forward, keep going forward until you see three fans, two at the side and one in the floor. Keep going forward until you come to two doors. Look to the left to see two blue pipes, in that opening is a multitool that only appears on easy and normal.

In the helipad room there's a crate containing 10mm ammo that doesn't appear on realistic.

There is a crate containing a multitool in the helipad room that doesn't appear on realistic.

Crate in the helipad room containing 7.62mm ammo that doesn't appear on realistic.

A clip of 7.62mm ammo in the new room next to the bilge pumps doesn't appear on realistic.

Follow the long paragraph for what I said for the multitool, but when you get to the two doors, go in. There's a crate there containing 10mm ammo that doesn't appear on realistic.

From the start go right, go down the ramp. When getting to slightly destroyed floor at the bottom of the ramp there should be a room to the right. Go in and to through the other door inside it. Inside it behind the pipes are two LAMs and two medkits. One of each doesn't appear on realistic.

The multitool on the desk by Dowd doesn't appear on realistic.

Two of the MJ12 troopers only appear on realistic.

There are three MJ12 troopers that only appear on hard and realistic.

There is one MJ12 trooper that doesn't appear on easy.

The crate with a biocell in it next to the security bot only appears on easy.

The crate with 10mm ammo in it next to the security bot doesn't appear on hard or realistic.

The crate containing 30.06 ammo outside the robot doesn't appear on realistic.

The lockpick in the last desk doesn't appear on realistic.

The 30.06 ammo on a crate doesn't appear on realistic.

One of the clips of 7.62mm ammo doesn't appear on realistic.

The 30.06 ammo in the storage area doesn't appear on realistic.

The biocell with the augmentation canister at the routing station only appears on realistic to replace the upgrade canister.

The augmentation upgrade canister in the same place doesn't appear on realistic.

The multitool in the kitchen doesn't appear on hard or realistic.

The multitool by the back door doesn't appear on hard or realistic.

The crate at the routing station containing a lockpick doesn't appear on realistic.

A crate containing a biocell on the door on the left on the street to the cathedral before the military bot doesn't appear on realistic.

A crate containing 20mm HE ammo in the building overlooking the street and cathedral doesn't appear on realistic.

The crate containing a LAM in the storage shed beside the cathedral doesn't appear on realistic.

A crate in the sewer containing 20mm HE ammo doesn't appear on hard or realistic.

In the police office one of the small cardboard boxes containing 20mm HE ammo doesn't appear on realistic.

The EMP grenade in Alex's room doesn't appear on hard or realistic.

The biocell in Alex's room doesn't appear on hard or realistic.

A crate containing 10mm ammo outside the top level of the elevator in the command building doesn't appear on hard or realistic.

One of the biocells at the hatch in the COMM building doesn't appear on realistic.

The 30.06 ammo on the roof of the COMM building doesn't appear on realistic.

The 7.62mm ammo at the hatch of the COMM building doesn't appear on realistic.

The rebreather in the cabinet on the stairs of the command building doesn't appear on realistic.
One of the packets of 10mm ammo in the cabinet on the stairs of the command building doesn't appear on realistic.

One of the clips of 7.62mm ammo in the cabinet on the stairs of the command building doesn't appear on realistic.

One of the medkits in the cabinet on the stairs of the command building doesn't appear on realistic.

One of the spiderbots at the start doesn't appear on easy or normal.

One of the crates containing a medkit as the bottom of the (non-flooded) stairs doesn't appear on realistic.

The crate containing a lockpick at the elevator doesn't appear on realistic.

The security bot at the bridge doesn't appear on easy or normal.

A crate containing 10mm ammo in the new off shore armoury doesn't appear on realistic.

A crate containing 10mm ammo at the bottom of the stairs on the main onshore building doesn't appear on realistic.

One of the biocells in the cupboard with the key guarded by a grown karkian doesn't appear on hard or realistic.

The lockpick in the open storage room guarded by a turret doesn't appear on realistic.

A pack of 10mm ammo in the locked storage room by the turret doesn't appear on realistic.

The biocell in the open storage room doesn't appear on realistic.

A multitool in the locked storage room doesn't appear on realistic.

A lockpick in the locked storage room doesn't appear on realistic.

A clip of 7.62mm ammo in the locked storage room doesn't appear on realistic.

The multitool in the cabinet guarded by the grown karkian doesn't appear on realistic.

One of the spiderbots at the start doesn't appear on easy.

One of the biocells in the administration area doesn't appear on hard or realistic.

One of the LAWs in the armoury downstairs doesn't appear on hard or realistic.

One of the assault shotguns in the armoury doesn't appear on realistic.

One of the assault rifles in the armoury doesn't appear on realistic.

The multitool in the building with a blocked door doesn't appear on hard or realistic.

The LAM on the elevator where Howard Strong is only appears on realistic.

One of the MiBs in the missile control room doesn't appear on easy or normal.

The EMP grenades where Howard Strong is don't appear on easy or normal.

The gas grenades where Howard Strong is don't appear on easy.

A dead MJ12 trooper with an assault rifle outside the sniper tower only appears on realistic.

On all other difficulties he has an assault rifle and lockpick instead.

One of the biocells in the Command 24 building doesn't appear on realistic.

One of the multitools in the lockers of the Command 24 building doesn't appear on realistic.

The biocell in the hatch of the Command 24 building doesn't appear on realistic.

The repair bot in the Tower 17a sniper tower doesn't appear on realistic.

The crate containing buckshot shells outside the new hangar doesn't appear on realistic.

A crate containing a lockpick in the building on the other side of the road of the new sniper tower doesn't appear on realistic.

A biocell on the ping pong table in the recreational area only appears on realistic.

One of the packets of soy food with the dead scientist in the barracks doesn't appear on realistic.

One of the scrambler grenades in the swimming pool doesn't appear on realistic.

The accuracy weapon mod in the lockers of the bathroom of the barracks doesn't appear on realistic.

The crate containing 20mm HE ammo under the stairs with the greasel doesn't appear on realistic.

The crate containing WP rockets under the stairs with the greasel doesn't appear on realistic.

One of the crates containing a medkit in the medical bay doesn't appear on realistic.

An empty cardboard box under the stairs with the greasel only appears on realistic.

One of the spider bots near the reactor doesn't appear on easy or normal.

A cardboard box only appears in the cabinet near Page on realistic to take over the space of the missing 30.06 ammo

An EMP grenade in a desk at the start only appears on easy and hard. Weird.

A multitool at the top of the cabinet in the medical area at the start doesn't appear on hard or realistic.

One of the assault rifles in the cabinet next to Page doesn't appear on realistic.

The 30.06 ammo in the cabinet next to Page doesn't appear on realistic.