Briar's Quest in KF2: I see a lot of confusion as to who PC Rob Briar is searching for whilst fighting zeds. Okay here we go, syntax analysis:
Quote 1: "Keep your eyes peeled for survivors. She must still be out there..." So Briar's motivation in this disaster is to find someone whose status is MIA. Neither confirmed dead and location unknown.
Quote 2: "That one's for Sophie, ya bastards!" Killing something / someone, then dedicating that kill to a person implies revenge. This line implies Sophie is dead, not the one he's looking for.
Quote 3: "I used to tell Sophie these places weren't real..." This sounds like something a man would say to a distressed wife or to his young daughter after having a nightmare. Again, this implies Sophie is dead, "I used to..." meaning she is no longer around. Coupled with the first quote, it further implies Sophie is dead, not the one he is looking for.
Conclusion: The manner in which he speaks these quotes, I'm forced to say Briar is looking for his daughter (or possibly a niece / sister), but the person in question being his own child is more romantic and standard for a tale like this, while Sophie was his wife, who was killed most likely during the disaster in Britain.
I should note that I believe it was Briar's bio in KF1 that mentioned his daughter being a hippy or something like that?
Specimen Lore:
The Scrake was noted in some tidbits to have been created to be a combat medic, able to withstand horrific amounts of pain, but eventually got a bit murdery from his obsession.
KFMod: Frankenstien-Esque. Chainsaw is rather long, specimen is overall dirty.
KF1: Doctor Esque. Tall and lean, but muscular. Chainsaw is more or less a standard chainsaw, just grafted onto an arm. Slow and methodical. Wears surgical mask.
KF2: Tall and Muscular, Doctor's apron is now a leather butcher's apron. Mask is metallic and when removed shows a really large mouth. Chainsaw seems purpose designed and is far more threatening.
The Gorefasts' tidbits are similar, somehow something missing an arm can become obsessed with pain and self mutilation, I guess? The various sketches in the artbook and voltor manor imply that the whole "Blade in arm" thing was thought out before hand, and not just sorta done on impulse.
The crawler was literally someone deciding to cross human and spider DNA. God help us when tripwire makes them able to walk on walls, by the way.
The Siren is a clone of Kevin's wife, sorta meant to be a weird homage to her dreams of becoming a singer.
Fleshpounds' gauntlets were originally meant to be restraints, although even without hindsight that frankly seems insane.
The husks were designed to be the perfect soldier, and were moderately successful, kinda. If I remember right, the first issue was that they were too stupid to operate their weapons properly, so the scientists decided to just chop a hand off and graft it on, but even then they were still pretty stupid and had a tendency to just shoot eachother for lack of other targets.
KFMod: None, generally assumed to backup idea that husks only popped up later on.
KF1: Patched in after some months. Makes an adorable "whrr whree" noise and punches as hard as a gorefast slices. Original husk gun available at trader.
KF2: Better at aiming, no longer makes adorable whrr noises. Also has no pants. Is able to shoot streams of fire from husk gun, as well as possessing a willingness to self-detonate.
Further Tidbits:
Foster's nickname (at least for himself) is "Fosty"
DJ Skully seems to be the same as DJ Scully, and he may or may not be the same as that skeleton costume bloke from KF1
Kevin Clamely (or one of his clones?) took a secret train from britain to france and proceeded to really mess up europe.
KF-Bedlam is the disused asylum where Skully was performing when the outbreak hit. It's assumed the music tracks specific to the map are his personal choices.
Foster is good enough friends with Skully to be willing to paint his mask into a homage
Donovan Neal is not a fan of Foster, evidenced by his belief that "Where I'm from, guys like Foster were locked up. Or put on TV"
Anton Strausser is implied to have been the former occupant of the open chamber in Voltor Manor's basement, near the trader.
Sir William Wiggins (Queen's Royal Guard character from KF1) is the cousin of Classic Masterson. This is directly stated.
Foster may or may not be a good day trader; bios seem to flip back and forth on this (Mrs Foster's explicitely calling him garbage at day trading). According to his KF1 bio karaoke is a big enough part of his life for him to note it in the title of his autobiography
Horzine is still actively developing weapons, from the Microwave gun to the entire line of medic weapons. Some of these seem to have been discontinued, such as the HSG-1 and the Z.E.D.
The trader pod prints new weapons using a 3D printer
The zeds may or may not have hit North America. KF-Suburbia explicitly notes that they have, although this has not been mentioned since.
KFMod's trader is presumed dead or missing.
KF1's trader is either dead, missing, or has been put out of business by Horzine.
Horzine's trader pod has more standardization; most tiers of weapon are the same cost, regardless of perk. Prices also remain the same regardless of the purchaser's abilities.
"Dosh" may be printer gel for the trader pod, explaining the ability to buy partial armor; the pod simply prints as much armor as it can with the amount of gel you give it.
The specimens transition from KF1 to KF2 has been accompanied by a complete lack of verbal training; zeds no longer possess the ability to speak complete sentences or even words.
The source of clots is an organism known as the Clot Mother; at least two can be seen in Biolab, growing in a liquid solution.
At least one Clot Mother is located in France; telltale tendrils can be seen in the extremities of the Catacombs.
A clot mother may or may not be located in Outpost; clone growth pods can be clearly seen in the sortie area while waiting for players.
Hans's lines imply he was present at Stalingrad.