Paint It Black: This happens at least four times in the comic. Vaarsuvius, Miko, and Durkon each receive one of these, while Belkar gets an inversion when given a temporary Wisdom boost. The title of the strip which has Vaarsuvius' transformation actually references the song/trope title as well, as V's robe is, in fact, painted black.
Palette Swap: Tarquin and most of his companions, as seenin someflashbacks. They change their colors according to the current nation they're "advising" (plus greying hair as they grow older), but keep the same design of clothes and/or armors.
The Pardon: Tarquin offers Roy one. Roy manages to get him to pardon Belkar, Haley's father Ian, and Ian's brother-in-law Geoff as well. Ian thinks it's a trick, though.
Passing Notes in Class: Haley combines this with Arrow Gram as a gag during the Azure city battle, the arrow hitting a hobgoblin mook about to attack Elan. Said arrow has a cute romantic note on notebook paper. Hinjo plays up the role of the exasperated teacher who takes the note and requests to see Elan after class, er, battle.
Belkar, who takes great joy in ending humanoid life, adopts Shojo's cat and is fiercely protective of it; it and the dinosaur he tames are among the few creatures he doesn't actively loathe.
Tsukiko likes the dead a little too much, trying to win Xykon's approval and viewing the undead she makes as her "children". Her reasoning? If Humans Are the Real Monsters, then the undead, as the opposite to the living, must be better.
Lord Shojo: As the gods pulled on the last few strands, the new world formed in the same planar space as the Snarl, shunting it into a tiny demiplane from which it could not free itself. The gods had been clever and built their planet to exist in multiple coterminous dimensions, thus blocking the only vibrational frequencies the Snarl could have used to escape from its cell. Haley: Huh? Vaarsuvius: He means our world is merely the padlock on the jailhouse door of reality.
Plot Armor: Being based on RPG rules, more plot-important characters tend to be higher-level and therefore tougher. Then-nameless Red Shirt Daigo actually manages to overcome a fatal injury simply by revealing his name.
Point That Somewhere Else: During Elan's first encounter with Tarquin, the latter bends Elan's rapier away from his face with the tip of a finger.
Poke the Poodle: In the Dragon Magazine comics, The Temple of the Shrouded Overlord believe that the Ancient Overlord will bring about a thousand year reign of darkness. To honor this despicable plan, they make a big deal out of forcibly extinguishing street lamps.
Polite Villains, Rude Heroes: Malack versus Durkon — at least that's how Malack seems to see it. Really, his attempts to find a "compromise" are selfish at best, and Durkon is infuriated by his assumption of the moral high ground when the dwarf had just caught him in the act of trying to turn his teammate into a vampire.
Literally. If Celia had explained that magic was required to break her talisman and summon her, Roy's death could have been avoided altogether. She assumed everyone could shoot lightning from their fingers.
Lampshaded (of course) and defied in a later strip, where Elan specifically tells Haley the whole story about Therkla, despite the fact that bardic tradition demands he "withhold it all so that at some later point, you can accidentally learn an incomplete version and jump to all the wrong conclusions, thus leading to entertaining dramatic conflict later in our relationship."
Girard Draketooth concealed the location of his gate from everybody and told them it was at a random spot in the desert, as explained in this strip. It really bites him in the butt when he failed to foresee that people who weren't Soon Kim might go looking for the Gate.
Vaarsuvius had a lot of opportunities to talk to Roy about the things he/she did and learned while Roy was dead. The planet inside the rift, for example, or Vaarsuvius' debt to the fiends. Either might have prevented the situation in "Two Paths".
Elan: Yeah right. Like I would use your crazy evil ring that you probably, like, tortured somebody to death or something to give it magic. Tarquin: Now, that is quite enough, young man. I am frankly offended that you would even suggest I would do such a thing to— Wait, who do you consider a "somebody"? Elan:Anybody! Tarquin: Fine, fine, I'll keep the ring then.
The Power of Legacy: O-Chul allows himself to be blamed for the destruction of Soon's gate to prevent further tarnishing of Miko's legacy.
The Power of Love: Elan telling Haley, "I believe in you," provides her with a circumstance bonus on her Open Locks roll sufficient to open a difficult lock, allowing the party to (momentarily) escape the Azure City prison.
In Start of Darkness, Xykon refuses to do any villainous scheme involving deflowering virgins. Because it's like giving a guy who doesn't know carpentry a hammer and expecting him to build you a house.
Belkar, after one of his shoulder demons convinces him that saving Hinjo's life will work out better for him in the long run than letting him be killed by an assassin.
Tarquin's teammates also display this. When he asks them to throw into a fight to kill most of the Order (in order to motivate Elan), they refuse because they don't think satisfying his personal "story" is worth their time, or the lives of the good soldiers he's already throwing away.
When Haley is stuck speaking in cryptograms, Miko tells her the gods have cursed her for her greed. Her response is a single four letter word and a dirty look. Since she has no other lines in that strip, it's impossible to decode what she said — could as innocent as "Ouch", or "Darn" — but it seems likely it was something rather more abrasive.
Pronoun Trouble: When talking about Vaarsuvius, others intentionally construct sentences to avoid pronouns, or use the nickname "V" in places where one would expect "he" or "she". V does get referred to by various genders, but Word of the Giant is that that's what the person believes. Taken even further with the brief look at V's mate and children, who refer to V exclusively as "Other Parent" as translated from Elven.
Attempted by Vaarsuvius in "Immaterial Components", when the wizard uses his/her Common Sense (caps included) to aid in the Banishment of an enormous devil which is in clear violation of the Square/Cube Law. Doesn't work.
Pun-Based Title: Four of the six books published so far. On the Origin of PCs (Charles Darwin's On the Origin of Species), Start of Darkness (Joseph Conrad's Heart of Darkness), No Cure for the Paladin Blues (the song, "Ain't No Cure for the Summertime Blues") and War and XPs (Leo Tolstoy's War and Peace).
Rainbow Pimp Gear: Defied Trope. There is a Running Gag early on that Haley is in possession of a powerful pair of magical Boots of Speed, but refuses to wear them because they're lime green. Later on she gets a tailor to dye them to match the rest of her outfit, but they still glow green when their effect is activated.
Roy to Miko, Vaarsuvius to both Miko and Belkar at the same time, Redcloak to Miko, and Hinjo to Miko (she really gets a lot of these, doesn't she?).
Xykon delivered a particularly nasty one to Vaarsuvius on the nature of true power. In general, this is Xykon's speciality.
And in #830, Redcloak to Tsukiko.
In #881, we get Belkar giving one to Roy.
Subverted in #500. Roy's about to launch into one towards his father, when he suddenly has an epiphany and decides that his father isn't worth it, since if everything he's been through hasn't made him want to be a better man then a few insults from Roy won't do it.
In #906 Nale gives a brutal one while killing Malack.
Recap Episode: Elan creates one for strip #864 because everyone might need a refresher after a 3-month hiatus.
Recursive Reality: Possibly. Inside the rift, there is a planet. What is on the planet is unknown. Common theories are that it's the original world supposedly destroyed by the Snarl, it's the Snarl itself, it's a new planet created by the Snarl, and many other theories. In the fourth book's commentary, Rich Burlew Josses the idea that it's our Earth.
Red Shirt: Played with, subverted, lampshaded, and played straight, sometimes within mere strips of one another. Redcloak, as hinted by his name, was originally supposed to be one, before being more heavily developed.
Red Shirt Army: Azure City's army, and most of the Sapphire Guard. (Except for members whose names are known.)
Reflexive Response: Haley gets to play with Tarquin's arrow-catching reflexes by firing two arrows toward his head while he's hanging on the railing of the Mechane. He does snatch both out of instinct, but doing so makes him lose his grip on the side of the ship.
Reforged Blade: The hereditary Greenhilt Sword, which got broken by Xykon during their first confrontation. Reforged with Starmetal, it's now a Plus Five Sword, with extra bonuses and neat glowy effects against Undead.
Subverted, as a jab at fan speculation, with Miko. Tsukiko gives a monologue about her intent to do this with the next body she finds... and then changes her mind when the first one she finds is in two pieces.
Malack attempted to turn Belkar into a vampire, but he was saved by a timely intervention from Durkon. Malack then proceeded to turn Durkon into a vampire instead; however, after Malack's destruction Durkon rejoins the Order.
Haley: You don't see us. Guard 1: Huh, must be a trick of the light. Haley: You don't work here anymore. Guard 2:Crap! How am I gonna pay my mortgage?! Haley: You are actually a yellow-footed rock wallaby. Guard 3: Screw this guard stuff, then. I'm gonna go find a wizard to polymorph me back.
Residual Self Image: Roy discovers that everyone in the afterlife "good" plane looks like their Residual Self Image. His father looks the same as he did when he died, an old man, because he always was a Grumpy Old Man, even when he was young. His mother, however, looks young and hot.
La Résistance: Best called just that, since they argue over the name. Moot point, now that Redcloak's wiped them out.
Restart The World: Downplayed. One possible outcome of The Dark One's plan is for him to remake the world with goblins as equals to the other races, but it's his backup plan if his main one doesn't work.
Resurrection Sickness: Standard for D&D, being raised from the dead costs a level, as mentioned by the Oracle. Roy also experience some trouble walking right after his own resurrection, his first attempt resulting in a faceplant, since he'd lost the habit of using his legs to move on the Material Plane.
Revenge by Proxy: Months after the party kills a young evil black dragon, the dragon's mother hunts down and subdues one of them. But rather than killing Vaarsuvius, she expresses her intention to take it out on V's children, instead:
Mother Dragon: After I am done speaking, I am going to teleport directly there, and then I will eat them alive. Slowly. Feet-first. I will then bind their souls to me with two necromantic scrolls that I acquired for this purpose. And I will disappear. I will leave this plane of existence, and you will never find me. I tell you all of this because it is not enough for me to simply kill you. You have taken my baby from me. I demand that you suffer the full measure of pain that I feel. As a parent, I am sure you understand.
Xykon: See? Never bet against the gullibility of the good guys, Redcloack. Redcloak: I had no idea you had put so many skill ranks in Reverse Psychology. MitD:Wait, what gate?
Roy manages to convince his father to help scrying the mortal realm from the afterlife... by refusing to beg him or even to get angry about his unwillingness. Eugene even calls it "reverse psychology" at one point... but he still falls for it. It's unintentional on Roy's part; he really no longer wanted his dad's help at that point. It's absolutely brilliant, too. Only a minute or two after Eugene tells Roy to screw off and go back the mountain to cry to his mother, he's scrying for him.
Eugene Greenhilt: Listen to me, young man, you will stand there and watch as I scry for you and like it, because I am your father! Roy Greenhilt: You do know that doesn't make any sense, right?
Revive Kills Zombie: As per D&D rules, "Heal" and related spells damage undead creatures, while "Inflict wounds" and related spells heal them.
Riding into the Sunset: Toward the end of Book 5, the Mechane, carrying the Order of the Stick, is shown flying into the sunset.
Right Makes Might: Hilariously lampshaded and subverted when Belkar attacks Malack and is certain he will win because "guys spouting corny lines like 'I have someone worth fighting for' always win for some reason", or something to that effect. Malack proceeds to incapacitate him with no effort.
Right Place, Right Time, Wrong Reason: When Vaarsuvius asks the Oracle how to obtain "ultimate arcane power", this is the answer given almost word-for-word. V sells a timeshare on his/her soul to three fiends in exchange for a temporary epic-level power boost. Although the stated motive was to save his/her family, V later admits that the only reason (s)he did it was because (s)he didn't want to ask anyone for help, and suffers (and will yet suffer) the consequences. The prophecy is fulfilled exactly as given.
Haley: ...she's a personal rival. She's ALWAYS gonna be the same level as I am when we meet, if not higher. (cutaway panel; Crystal is playing cards when a "DING!" appears overhead) Crystal:Sweet! Starshine gained another level!
Lampshaded in the title "Don't Question the Color of the Bag"; a joke in the strip has Roy's usually-useless Bag of Tricks unexpectedly materialise a rhinoceros, which lands on top of him. (In the game, there are two differently-colored Bags of Tricks, one of which spawns small rodents, and the other larger animals, rhinos included.)
The major characters have no explicitly stated levels, stats or ability sets (other than rare exceptions, like Elan's 18 in Charisma or V's 18 in Intelligence) because that would restrict the jokes. Their stats can and have been guessed based on their actions in the comic, though.
Running Gags include Elan's dubiously-helpful bard songs, V's creative application of explosive runes and ambiguous sex, Durkon's dendrophobia, Xykon not remembering Roy or his dad, Daigo "saving" his last name, the Mit D's constant confusion about the Gates, the practical implications of Sending spells (you try getting everything across in exactly 25 words), among others.
Flumphs conveniently cushioning people's landings... or not.
"... the whole kobold-head-into-an-object thing is sort of a running gag with me."
The title of the strip is a definition of a word prominent in the punchline.