It's a bit hard to tell, but Doc's appearance, along with the other regulars, has been refined since the beginning strips.
A much more significant one happened the final time Roger pushed the Schmuck Bait button; the comic was entirely black-and-white up to that point.
Artifact Title: The first five strips were doodled on a whiteboard, before he changed to using a computer to create the comic. There was a sixth one on the whiteboard, but after that, the titular medium has never been used.
Before that, Doc fitted a regular M2A3 Bradley IFV with a hot tub, complete with girls and probably an entertainment system, as a gift for the Army after the Real Life capture of Saddam Hussein, in 2003.
Big Eater: Doc, granted he is a polar bear but once he ate an entire deep-fried walrus.
Big Lipped Alligator Moment: To celebrate the 1500th strip, a big can-can line appears out of nowhere on Red's paintball field with most of the main cast, leaving behind some debris in the last panel along with a very confused Pirta. invoked
Bland Name Product: If you look closely at the background, you can see Doc carrying a Khil chainsaw, while more recently Jinx can be seen with his brand new Khil Jr. chainsaw. Clearly a pastiche of Stihl and Skill power tools.
Blinding Bangs: Without his hat Swampy is too similar to Red. Here the author tries a new look.
Brick Joke: A long time coming. Early on in the comic, Doc makes a comment about how he keeps a bone around for anti-cheating and safety lectures, so people take his threats of eating them seriously. Cut to a few years later, when Bandit recalls his first experience with paintball...
Butt Monkey: Swampy regularly gets stapled to the ceiling, among other things.
Caffeine Bullet Time: Done fairly realistically in one arc. Doc has to wear goggles in order to see in the wind-tunnel-like air friction, and causes objects he exerts force on to blow to pieces. He even accidentally plows through several buildings. Of course, it's started by a quart mug of energy shots.
The Cameo: Nearly every Halloween, other comic characters show up for Doc's party. The list is extensive.
Carnivore Confusion: Averted. Rainman wanted lettuce on his half of the pizza. Swampy wanted fieldmouse and ground squirrel while Jinx wanted lemmings.
Cool Garage: The first one was Doc's shop, but now the Emergency Response Center has one of their own, mostly to house their giant fire truck.
Comically Missing the Point: When Sandy is railing against "upgrades" done to her car by Doc (which include offensive weaponry) in this strip, he insists on pointing out the difference between rockets and missiles (unguided versus guided), a launcher for the latter mounted on her car.
Conjoined Eyes: The "generic" anthro furries that have more or less replaced the featureless "bubblehead" no-neck humans all tend to have conjoined eyes, although much of the older, more regular cast have eyes that are separate from one another.
Double Standard: Abuse—Female on Male: The male characters are quite free to beat up other male character and the female characters are quite free to beat up male characters, but no males have been seen or mentioned as beating on females. This strip and the one after it shows that Pirta hit Doc hard enough for him to have another near death experience.
Duct Tape For Everything: Doc uses duct tape to fix anything, as well as using it to remind people not to take off their helmets during a paintball match. Usually because he can't find the stapler instead.
Exactly What It Says on the Tin: In this strip, the title of the movie the gang is going to see isn't stated, but Roger points out that "guns, fast cars, and explosions" are specifically mentioned in the title.
The Faceless: Swampy, who is almost never seen without his face obstructed by his hat or some object, and almost every human character, by virtue of having indistinct circles-for-heads.
Failsafe Failure: Things blow up regularly in this webcomic. One of the reasons for this is that the fail-safes never work in this comic.
Four-Fingered Hands: In the first few strips, Doc was depicted with 5-digit hands, but shortly after the strip's name became an Artifact Title, the character design was changed to have 4-digit hands, with a note by the author explaining the change.
Furries Are Easier to Draw: The humans are drawn as people with floating heads. The non-human cast is drawn somewhat better, but only somewhat. The animals mouths are seldom seen, even when they're talking. They're usually only seen if they're shouting. The technical and mechanical devices though, oh-ho, they're drawn exquisitely! According to several posts by the author on the TWB forums in August 2011, however, he's using more detailed humans to get more practice with drawing them, and moving away from the "floating bubble heads".
Gangsta Style: A custom work order for a paintball marker has the ammo bin put on the side, so that when held this way it can feed the paintballs normally. Doc and Roj seem unimpressed, but hey, it's work.
Gender Bender: After pressing a button with a Shmuck Bait warning sign, in the May 22, 2012 strip Roger is transformed into a woman.
Genius Bruiser: Doc easily qualifies, being built like one would expect of a polar bear, and who builds things like pizza teleporters, mecha, and reality-altering devices (as a paintball gun!) as a hobby.
Girls With Moustaches: Sandy greets a customer to Doc's shop, and is told by the customer that he wants to deal with a male employee. She ducks behind the counter, and comes back up with a fake moustache on her face, asking again if she can help him.
Halloween Episode: There's almost always has a Halloween-related story around October. Mostly it's just parties where Cameos from other webcomics abound, but on occasion it's a full story arc, like with the 2010 Zombie Apocalypse story arc.
I Have a Family: In this strip, after watching an awful movie Doc threatens a janitor with violence over it. The janitor pleads for pity on account of having three mouths to feed. Two goldfish and a gerbil, which is sufficient to get the janitor off the hook.
Insane Troll Logic: According to Doc, he won't need a parachute when he next goes skydiving. He'll just bring along an extension cord or some welding leads, and it's an even bet that they'll snag on something before he lands.
Interspecies Romance: Jake (skunk) and Pirta (snow leopard), Kasi's mother (Cheetah) and Howie (wolf).
Klatchian Coffee: The crew of The Whiteboard, after (or in the middle of) a particularly interesting New Years' party (and that's saying something), manages by accident to create a coffee strong enough to cure astigmatism, boost intellect, and add a cup size to women. The effects are temporary.
Lad-ette (or at least Tomboy): Tawny hints at this — Wrench Wench, fond of trash talk, absolutely ruthless on the field, and generally pretty badass. (Although Pirta and Sandy aren't exactly girly-girls, they certainly look it in comparison to Tawny.)
Limited Wardrobe: Doc's closet is shown to be filled with almost nothing but black T-shirts. In a Fourth Wall Mail Slot comic he later explains that it's because they're cheap and hide grease stains.
Ms. Fanservice: Pirta, in-universe at least. The fact that she favors scanty clothing (even in Alaska) and her feline anatomy means she's always walking on her toes (and therefore looks like she's always wearing very high heels) may imply this for real life readers as well. (Considering Doc is at the very least... fascinated... with her, this is not likely unintentional.)
Goes to ridiculous levels when the refrigerator full of Mountain Dew is crushed, the coffee machine wasn't fixed from its last misadventure, and Doc resorts to drinking energy drinks. By the 5-gallon bucket.
Improving coffee machines is high on Doc's activity list. Like when having found a BMW motorcycle engine.
Near Death Experience: Starting here, though a bit unusual as the manifestation is telling him he should have died. A long time ago.
"Son, you use high explosives just to make breakfast. We're amazed you made it past puberty."
Non-Mammal Mammaries: Pretty much all of the regularly depicted female funny animals (all based on mammal species) are rather well endowed with human style breasts, which isn't treated in the comic as being unusual in any way.
The Noseless: Just about every human drawn in the comic has a mostly featureless "bubblehead" head, with noses being one of the details left off.
Nostalgia Filter: Sent up in the paintball domain starting here and in the next strip, comparing paintballing in the past to that in the present.
Or, in the cases of Sandy and Pirta, sane women. They are the only ones who don't take the other character's antics in stride.
Now that she's gotten a proper arc, Tawny is in this role too as the counterpoint to Snowshoe.
Jake, in almost every situation, is far more level-headed than his friends, and is often frustrated by their extremes (see Roger dragging him off during the PvP/The Whiteboard crossover). Still, he likes to play with machetes.
Orwellian Retcon: Roger pushed the button for the final time (according to Word Of God), and most comics from the previous six months suddenly developed color. Roger is unaware that anything has changed, and by implication, the other characters are also unaware (or are they?)... and even that particular strip got retconned; it first appeared with the first two panels in black and white and the third in color.
Pyrrhic Victory: In this strip, Roger describes the aftermath of an indoor snowball fight (It Makes Sense in Context) as being a Pyrrhic victory after the use of a snowblower results in Doc's office getting three feet of snow dumped into it.
Happens to the strip, from time to time. Usually accompanied by a filler cut-and-paste strip in which characters look like flounder with both eyes on the same side of their heads. Recently the author started using regular strips (like this one) with text replaced to some out-of-canon gag. Also accompanied by an explanation for why that day's strip isn't up. The filler strips never appear in the main archive, but some of the flounder strips can be seen here.
Shmuck Bait: In this strip, Roger is presented with a button with a warning sign reading "For the love of God do not push this button!", as a filler strip. Doc Nickel invited readers to suggest the results of pressing the button, and got several hundred replies (after expecting only a dozen or so). Strips illustrating the suggestions were usually posted on Tuesdays and Thursdays.
Shout Out: Quite a few of them are for fairly old movies and old TV series:
Teleporters and Transporters: Doc made a "Pizza Teleporter" so he could get food in seconds. Unfortunately it only teleports to a specific spot on his counter, trying to send it to say, the field results in the toppings and crust separating or cheese blocking up an engine.
Time Stands Still: Gained in a super-speed version by Doc at one point due to too many caffeinated energy drinks. We first see the world from everyone else's perspective involving multiple things (that Doc had touched) exploding and Doc suddenly being found several buildings over with multiple broken walls between his origin and destination. Then we see Doc's side of the story. While he doesn't have to deal with light shifting and air friction isn't much of a problem, he does have to deal with lack of friction between his legs and the floor and with inertia, both that of other objects and his own.
You Do Not Want To Know: A common reaction by the regulars when Sandy or Pirtanote moreso the latter, not having been around the gang for as long as the former asks about any particular weirdness happening.