Female Gaze: Guinea's transformation provokes some... reaction from both Ellen and a female trooper. The next page has the latter blushing and demonstratively looking away while the Uryuom trooper, obviously, comments on this.
Ms. Fanservice: In just about every one of her appearances, Amanda ends up transforming, usually shrinking or turning into a Half-Human Hybrid. This appears to be Fanservice for a particular segment of EGS's fanbase and Dan himself.
The Nudifier: Dr. Germahn once invented a potion that caused your sweat to dissolve clothes.
Playboy Bunny: This is the first bit of Fanservice Shive gave us (as well as what he claims is "the first and last violation of the 'No Cleavage' part of Sarah's contract").
First Girl Wins: Tedd and Grace (that we know of anyway), Ellen and Nanase, if you count Ellen's "birth" as taking Sarah out of the picture.
Fish Out of Temporal Water: Abraham averts this by having spells that give him modern knowledge and clothes; given how magic works in this series, it makes sense that he would have them in conjunction with his statue spell.
555: Sarah's number is 555-7272. Another number mentioned is 555-3239.
Flat Joy: When Elliot discovered that his inconvenient "girly powers only" time ended and he began to acquire cool magic. Of course, he's not only in a female form, but in the middle of a random encounter, but still.
Flight: Many characters are capable of this. Nanase, in three different ways: wings in her fairy form, magical levitation in normal form, and wings in her "angel" form. Grace — levitation, though only in Omega form. Nioi — magic. Vlad — wings plus levitation. Immortals (so far, all) — either magic or it's an inherent quality. Elliot — while in his superhero form.
Follow the Chaos: Need to know if Tedd is upstairs or downstairs in his lab? Listen for an explosion.
The Force Is Strong with This One: Adrian Ravenadmitted having ability to measure magical power without devices, which all but confirms a common wild guess on who his "random favourites" are. Later was explained he can sense magic from people...through his ears. Smell, precisely. Don't ask.
Forced Meme: Shive attempted to turn "sexy awesome" into a catchphrase, but never caught on outside the fan base, and even the characters have all but stopped using it.
What's seen here translated with this. "Death. It Is Time For The End Of Man. This Master of Fire Shall Inherit The Earth. My Very Presence Eats Away At Your Flesh" Other than the two bizarre words in the end, it's pretty creepy.
Way back in 2004, a non-canon sketchbook had some female characters as kittens, with Ellen explaining "Dan has wanted to do a story with me as a cat since 2002, but he backed away from it to keep the transformation gun from becoming 'overpowered'". Six years later...
Fourth Wall Psych: In one strip, Tedd appears to be commenting on a stupid mistake that Elliot made despite not being around to witness it. However, he is quickly revealed to instead be commenting on a similar situation in the sitcom that he was watching, meaning that he was merely Leaning on the Fourth Wall rather than breaking it.
Freak Out: Susan wasn't amused to discover what the hammers were made for — and what they in fact do. Of course, that being in the presence of an Immortal, she just caught an Instant Sedation spell in the face and got spaced out for her efforts.
Freudian Excuse: Most of the cast have really screwy home lives. Specifically, Susan's hatred of men is very nearly outright said to be her making an excuse for her father cheating. Her mother's hate-filled "because he's a man" when lil' Susan asked her why probably helped this along a little.
Functional Magic: Nioi is a powerful sorceress, as is Nanase. Nanase in particular uses it very often and quite openly at times.
Magic A Is Magic A: A significant portion of the "Sister II" arc is devoted to explaining exactly how magic works in EGS.
Squishy Wizard: Specifically averted. Two of the three wizards seen so far are also swordsmen (Abe also used shield and axe), for third it's unknown, but as a FBI operative he's likely to have at least basic handgun training. The rest of magic users in the comic practice Supernatural Martial Arts, and one that doesn't is at least pretty badass and is competent enough with melee weapons.
Wizard Duel: Magus vs. Terra's duel appears to be either sparring or a non-lethal quarrel. Abraham vs. Raven, with spells and weapons both.
And Mr. Verres already contemplated using swamp gas as a random coverup.
Gender Bender: The entire main cast, at least once. They even did this as a theme for a birthday party. Ellen is a special case, since she's an Opposite-Sex Clone of another main character with all the memories of the original, and she has the innate ability to turn men into women. Pretty much anything in the EGS universe will get your gender bent, including fixing a toaster.
Pretty much whenever anyone is transformed, goes in both directions. It helps that the person behind the gender-bending technology is an unrepentant pervert who custom-designed transformation variants to appeal to certain fetishes.
This issue was explored in rather disturbing ways in one of the Q&A sessions.
EGS, while not as casual or frequent about it as The Wotch, certainly pays the Law its dues. According to the rules governing the comic's main sex-changing phlebotinum, only male-to-female sex changes can be made permanent (pregnancy); female-to-male sex changes, even of someone trapped by pregnancy (for whom it's only even possible afterwards), cannot exceed a 30 day time limit. The second time a boy - the main character - is turned into a girl the device breaks, leaving "her" stuck for the full thirty days; the attempt to circumvent this creates an Opposite-Sex Clone and the permanent ability to change sex at will, something the rules of magic eventually force him to do on a regular basis.
Also, much later, a "seyunolu" (chimera) member of the Quirky Miniboss Squad, Vlad, is hit with a Transformation Ray and is turned female, but more importantly to him/her, human. "She" has no desire to change back, and since Bizarre Alien Biology overrides the time limit (and, implicitly, gender identity), Vladia, as she is now called, is treated as a woman from then on.
Moving on from Elliot being a double victim of this, we get to Tedd. Who probably wouldn't know this was a law: the "circumstances" usually equate to "Dad's out of town" and "As a girl, I'm hot."
Largely averted, despite all of the constant Gender Bending: Elliot has no interest in remaining female for long and considers his gender-bending Power Incontinence distasteful, Justin specifically rejects the idea even though it would make him sexually compatible with the object of his unrequited affection, Ellen accepts it without expressing any preference (though there are hints that the Loss of Identity associated with Opposite SexCloning Blues was a sore point until she got a new set of memories). Zigzagged as of "So A Date At The Mall, where Elliot implies he's at least mildly gender fluid and admits that having a cute, sexy superheroine form is pretty damn cool.
It's touching in Vlad/Vladia's case. There's nothing kinky about her accepting the change — for the first time in her whole life normal people aren't terrified by the sight of her, so she's willing to accept any form provided it's human, which her old, male form decidedly was not. And given that her one attempt to use her supposed shapeshifting powers was a painful, near-death experience she's not about to experiment even given the chance.
The current theory is that Elliot will acquire new female forms again and again until he really likes one of them — then again, it was Tedd's idea. Between flying around as a superheroine and ogling Perky Goth form in a mirror, he may have found this already.
Tedd is the only straight example. He likes this form of shapeshifting because his androgynous face becomes an advantage while close enough to Tedd's own form and he likes to feel attractive. Once this problem became moot it was revealed that Body Swap is #37 on his fetish list. Later on justified when Tedd realizes he's gender-fluid, but was uneducated on non-cisgender orientations. He just has access to technology that allows him to shape-shift when he feels more like a woman than a man.
And when Pandora does ... something that causes him to transform? The response is a BIG smile. And a gripe that her opponent in the card game, who keeps hitting on her, is 'totally ruining the fun of being inexplicably turned into a girl by some terrifying unknown power'.
Grace's Birthday Party arc, part-masquerade where the various characters deliberately chose stereotypical outfits for each other in keeping with the 'walk a mile in my shoes' theme of the occasion.
Susan starts acting macho and aggressive to Nanase very soon after becoming male. Sarah points out that Susan is simply a highly competitive person; now that she's male, and feeling stronger, it takes the form of an arm wrestling match.
Tedd does note that the first few times anyone is gender bent, their thoughts will be exaggerated, which played a part in everyone's storyline during the event, but the only one whose gender bending mental state was a major plot point was Susan, as it helped her recognize her hangups with men.
Later, when Elliot develops the power to morph his clothes and appearance along with his gender his female forms tend to end up wearing girly outfits because he apparently just can't help visualizing them that way.
Elliot's superhero spell comes with a "party girl" form whose default state is hyper and apparently slightly drunk.
Genre-Busting: It crosses a few. It starts out like a comedic slice-of-life comic, quickly adds sci-fi and drama, then fantasy (later explaining the sci-fi as magic)(except it's not the same magic). Currently it's kind of a mix of the lot. And weird.
Justin, from Rhoda's point of view. She's normally scared of people bigger than her (and his 6' to her 5' is quite a difference), but also knows that he's friends with Nanase, and that Nanase wouldn't be friends with anyone bad.
Sensei Greg is an imposing 6'10'' (208 cm) but is a perfectly decent guy. So decent, that he is bothered by not being a "traditional" perverted anime sensei.
Good Is Not Nice: Raven is a strict disciplinarian, quite caustic and doesn't suffer fools gladly. He's also a ruthless fighter, and won't hesitate to risk his life to protect his students.
Girl of My Dreams: A realistic twist on this. Elliot dreams of Tedd turning into a girl and then the two kiss. However, he doesn't remember the full dream, in particular who he had kissed. So when he first encounters Ashley he mentally fills in the blank and thinks that she was the one he kissed in his dream.
Grandfather Clause: Several of the boys originally had very '90s/early '00s hairstyles; while Elliot's mullet and Justin's bowl cut have been toned down to generic medium-guy-length hairstyles. Tedd's curtains lasted longer, but as of Squirrel Prophet, he's got, to quote George, "cute girly fairy hair."
Mr. and Mrs. Dunkel are capable of taking the most bizarre things in stride, to the point where it becomes a Running Gag.
Mrs. Dunkel: Why are there two Brownies? Ellen: I'm Ellen, Mom. I turned into a cat. Mrs. Dunkel: Oh dear. Can you change back? Ellen: Sure, anytime I want. Mrs. Dunkel: That's good.
It's implied that Tedd has been doing some WEIRD stuff to and involving Elliot for years, meaning they might just be used to beloved family members becoming small furry animals (or something equally bizarre) on a regular basis. Perhaps they had a bigger reaction the first time something happened, but since there was no permanent harm from it, or any of the subsequent incidents, they've learned to roll with it, even as it eventually escalated into Ellen's birth and Elliot becoming a costumed superhero.
Hard Head: Lampshaded here. Upon learning that he was knocked out by a blow to the head, Elliot starts worrying about brain damage, but Tedd tells him he's overreacting.
High School: Two of them of the cross-town rivalry variety, complete with uniforms, bizarre teachers, odd mascots, and most of the other associated tropes. Half the cast attends Moperville North and the other half goes to Moperville South.
Hybrid Power: The Uryuom breeding method pretty much inevitably results in this. Uryuoms frequently have several parents adding their genes to an egg, as they don't have typical genders. This ultimately results in a character being a hybrid of four different creatures, conserving many of their powers.
Dan lampshaded his reasoning behind changing the hammer origin in the later story arc. The old guy who looks vaguely like Santa explains his initial reasoning for using the hammer gag to humorous effect... that is, the same as out of the 'verse.
Grace had shades of this at first but quickly let go of this, and once she did start a normal school life with Ellen, Nanase, and Justin, she actually found it a little restrictive.
Vlad is abnormal even among shapeshifting chimera in that he was made using the DNA from so many different animals that he can't transform without risking death. This leads him to be jealous of his "brothers" ability to transform into human forms and blend in with society. He gets his desire partially fulfilled when he is transformed into a human woman by Ellen's beam becoming Vladia.
I Just Want to Be Special: Sarah has a bit of this, mostly because she couldn't spend so much time surrounded by shapeshifters, magical martial artists, and mad scientists without getting jealous or at least curious.
The "I Love You" Stigma: Elliot always considered himself and Sarah to be Like Brother and Sister, but when Sarah say "Love", he didn't want to break her heart so he started to date her, trying to never include any lustful and sexual emotion.
The Immortals are basically spiritual beings who never die, but the way they go about it is almost a deconstruction of the concept. They continue to get older, smarter, stronger, more bored and less sane until the point comes where they basically become Persons Of Mass Destruction. To prevent this, they voluntarily undergo a kind of ritualistic death/rebirth cycle every couple centuries to lose most of their power and memories so they can start over and keep things interesting. Which is a good thing, as Pandora Chaos Raven (name chosen by self) shows to full extent with her crazy, and Eldritch Abomination / Creepy Child forms...
Ironically, half-immortals (elves) largely have the advantage over true immortals. Since their power is not constantly increasing like their parents', they don't have to worry about resetting, but get ageless immortality and powerful magic. The only downside is that they are bound by similar rules as the immortals, meaning that they can only interfere directly when a situation involves magic, or to defend themselves and others.
Raven: You are a homicidal wizard attacking a school. No one will care if I kill you.
There are also various "aberrations" that immortals ruthlessly destroy, who obtain a pseudo-immortality through either body stealing or parasitism.
Immortality Hurts: In Wrath Of God, Nanase must keep Abraham from killing Ellen using only her Fairy Doll and Fey Punch spells. Because she feels everything that happens to the dolls as if it had happened to her own body, she is essentially hacked to pieces over, and over, and over... The page is titled To Die a Dozen Deaths
Ineffectual Sympathetic Villain: Technically, Magus apparently was behind the v-five Elliot incident and tries to manipulate Ellen within some plot that sounds quite dubious. And is not very good at this. But he's in desperate straits, which isn't even his own fault (unlike Abe's case). And he's still reluctant to kill a guy who stands in his way even when pushed hard to do this. He knows it, too.
I Never Said It Was Poison: Susan was already starting to grow suspicious of Tom 's behavior, but it comes to a head when she realized he apologized for missing her online the night before. She hadn't said for certain that she would even be on, concluding that he had been online, but in invisible mode.
I Never Told You My Name: Painted Black arc. After Elliot is captured he refers to Guineas by name. Guineas then tells Hedge that Elliot knew his name even though he hadn't been told it. This causes Hedge to realize that Elliot must know Grace, who's the only one who could have told him. Hedge then turns this around on Elliot by only referring to Grace as "my sister", so when Elliot refers to her by name, it proves Elliot's spoken with Grace since Elliot and Hedge first met.
Info Drop: Sarah's last name was revealed in this manner; the principal used it to refer to her while rebuking her for breaking the dress code. The name? Brown.
Infodump: Shive is really thorough when it comes to describing the capabilities of Tedd's technology, the mechanics of alien and hybrid genetics, and more recently, magic. Anything left for the readers to guess about is practically guaranteed to be a Chekhov's Gun.
The so called Trapped in the Basement portion of New and Old Flames (so-called due to the just under two months real time spent infodumping in the Verres' basement) and the entire Hammerchlorians arc (essentially an entire arc devoted to nothing but infodumps and backstory exposition for Susan and her summoning abilities) are probably the most notorious example of Dan's tendency to slip into infodump territory.
Informed Ability: Susan's magical powers, which are seen exactly once and then aren't visible for many arcs. Then Susan explains that Nanase's powers are of a different order than hers ("Awakened" vs. "Dreaming") without going into detail. Until much later Susan explained her magical abilities with a big flashback. and she is properly "Awakened".
Interspecies Romance: Tedd and Grace; Ellen @ Second Life and Archie; the demonic duck also admits to preferring human women. For Uryuom it's quite normal to create chimerae, fertile at that. Isn't done obliviously, as at least psychophysiology matters even with shapeshifting seyunolu.
Ironic Name: Tiffany "Susan" Pompoms always goes by her middle name, because she considers her actual first- and last-name to be too "perky and upbeat" for her cynical, sardonic personality. (Ironically, it's been made quite clear that if it wasn't for ONE traumatic childhood event, she would've wound up fitting her name just perfectly.)
Elliot and Nanase's relationship had no spark and eventually failed, and she couldn't explain why...until Ellen.
Though this trope is never actually invoked and the trope will probably never be played straight in this case, but Elliot and Tedd's odd connection twists it. It seems like in any universe where they were born opposite genders (such as one where Elliot has always been "Ellen," and the technically non-canon story where Tedd accidentally and retroactively became "Tess") they are inevitably dating. An exception was the world of "Second Life", but even then Tedd has a crush on her and she, while Oblivious to Love, considered him a good friend.
Kaleidoscope Hair: Happens to Nanase (whose hair turns black when her magic burns out) and Susan (when she goes through an angst-induced awakening)
As a practitioner of "anime-style martial arts," it's no big surprise that Elliot (and Ellen, who "inherited" his abilities) uses a variety that emits short-range force blast. He needs to have free hands to do it.
Ellen has a variant with shooting beam from her hand. Sensei Greg is, of course, jealous when he sees it. It turns people into attractive girls, and lately can turn HER into whatever she hits.
Knight of Cerebus: Damien. It's sort of a subversion as Dan killed off Damien because he didn't want his comic to develop Cerebus Syndrome. It did anyway, just with seriousness developing within the characters' personal demons rather than fantastical conflict.
Life Drinker: The monster in France was a former human who achieved immortality by draining the lives of young women.
Lighter and Softer: One chapter is titled, "Bringing Silly Back." It starts off substantially lighter than the previous chapter about life and death struggle with a simple arc about a race through an IKEA parody. Then, after "Hammerchlorians" explores some of the darker parts of Susan's backstory, "New and Old Flames" followed it up with a goofy super hero story
Long-Runner Tech Marches On: In Shade (2002), Elliot had a landline phone extension in his room (with then-old-tech corded handset); later on all telecommunication among the teenage cast is via cellphone and even adults are shown using landlines only at their workplaces.
At the beginning of Grace's birthday party (2005), Sarah gleefully details the specs of the digital camera with which she intends to document the evening. A 512 MB memory card and a computer with "gigs" of space to back up said card onto means lots of pictures, sure, but it also looks positively quaint next to the phones some characters are using much more recently (and within less than a year of in-universe time).
Susan still works in a video rental store, despite them being very rare these days.
Love Dodecahedron: Among the main cast many have shown a obvious attraction to more than one of their friends, even if they don't ever plan on acting on those feelings. Then once you add the occasional side character with an attraction to someone from the main cast it can get pretty confusing as to who likes who.