Laxus, though how much of a Face he was to start with is debatable.
The entire reason Oración Seis seeks Nirvana is the ability to cause these at will in whoever they want.
Gray in the anime exclusive arc, though he's more of a Fake Defector. It turns out that Natsu forgot a promise to the villager that was sealed by Daphne and he kind of wanted him to destroy Daphne's artificial dragon.
Then there's the "Welcome to Fairy Hills!" special chapter. It IS fanservice in forty pages with a little plot in between, though it has plenty of Character Development for the female members we don't usually get to see.
Fan Service with a Smile: Team Natsu briefly work in a cafe at one point. Lucy and Erza have ridiculously sexy outfits, and Gray forgets his uniform save the bow tie.
A Father to His Men: Master Makarov is very much this. Phantom Lord kidnapping and hurting three of his "children" was what finally drove him to defy the law against guild fights and teach those belligerent jerks a lessonthey never forgot. Gajeel has had roughly ONE MOMENT of Oh Crap. This is a guy who taunts Natsu for fun. What makes him brown his trousers? Angry Makarov. What was he doing? Inviting Gajeel to join Fairy Tail.
Makarov: But so is abandoning a young man surrendering himself to darkness.]]
Feed It with Fire: Dragon Slayers can regain energy by eating their given element (though not any that they create). Some, such as Gajeel the Iron Dragon Slayer and Wendy the Sky Dragon Slayer, are more fortunate than, say, Laxus (lightning) and Cobra (poison). Though Cobra was smart enough to keep a poisonous snake so that he wouldn't have to rely on luck to refuel.
Final Boss Preview: Done very often. Zero's first act is to beat the shit out of Natsu. Laxus did the same thing, although he was only stunned. Reitei Lyon's first appearance has him using Gray as a soccerball. Hades' first fight is curb stomping Makarov. Subverted with Phantom Lord when Jose turns out to be an illusion, and Makarov is taken out by Aria's sneak attack.
Finger Gun: Hades does this after he shrugs off Team Natsu's combined efforts. Naturally, he kicks the crap out of everyone with it.
Laxus and Mystogan are both S-class wizards that don't spend much time in the guild. Laxus is a flashy JerkassSocial Darwinist who thinks he's too good to hang around the weaklings in Fairy Tail, while Mystogan is a Shrouded in MythMaster of Illusion who is ashamed of where he comes from and wants to thwart his father's plan to turn this world's wizards into Lacrima. Laxus dresses in flashy clothing, such as a fur lined jacket and a royal purple shirt, while Mystogan wears baggy clothes in black and gray.
Another foil for Laxus is his grandfather, Makarov: a wise, humble old man with the power to flatten a city, who prefers not to fight except as a last resort. Makarov has a habit of downplaying how much of an effect his guidance has on his highly successful guild, and attributing it all to the members.
Natsu and Gray are an obvious example. They're quite similar in age and temperament, but use opposing types of magic, and Natsu is Hot-Blooded and impulsive while Gray is more thoughtful and methodical.
Erza and Lucy. They're both young, attractive, and want what's best for their friends, but Erza is a calm and collected S-class wizard who fights with melee weaponry  and Lucy is a summoner who's always freaking out over something.
Erza and Mirajane: They're both the same age, a little off and were constantly bickering with each other and later they're both the relative Team Moms of the guild while Erza is the stern one while Mirajane is the bubbly one.
Foot Focus: Seen quite a few times in the manga, especially in the Edolas arc. Lucy and Erza tend to get this treatment.
During Erza's fight with Evergreen, she takes off her shoes (and long socks) so that she may hold an additional two swords with her toes.
Gemi and Mini show up in a couple chapter covers long before they were ever introduced. Though since they just look like a couple of odd creatures (never too surprising in Mashima works), it's easy to just pass over them.
In the last shot of the anime's second opening, Loke is seen standing behind Lucy and next to her Celestial Spirits... I wonder why?
Episode 4 ends with scenes not in the manga, including a battle with enemy wizards, one is a fortune teller who predicts that Gray "will have problems with water and women." Does that remind you of anyone?
Added scenes in episode 26 hint toward Loke being a Celestial Spirit.
If you notice the cover for the 197th chapter Edolas Lisanna isn't part of the Edolas Fairy Tail guild waving goodbye. Why is that? She's actually Earthland Lisanna!
Remember how Gajeel wanted a cat before the beginning of the Edolas arc? Guess what he got at the end of that Edolas arc. In extension, the anniversary of Lisanna's "death" Anniversary just happened to be arriving right before the Edolas arc. Guess who shows up while Mirajane and Elfman are visiting her grave at the end of the Edolas arc.
The anime adds in a scene where Gajeel's action figure has a place on it's stand for a small cat. The Natsu/Happy and Wendy/Carla figureines are sold in pairs, so they figure that Gajeel is eventually going to get a feline companion.
Natsu telling Zalty (Reitei Lyon's Dragon) that he smells like a woman. Zalty is actually Ultear in disguise.
The last page for Chapter 234, a seemingly out of place page with a boy, who resembles an older Romeo, staring at the sea; he appears again in Tenrou Island arc's ending marking the beggining of a 7 year Time Skip, the year is X791, this date could be seen in the boy's next appearance on the newspaper next to him.
Forgotten Fallen Friend: Subverted. Though Simon and Ur both seem to quickly vanish from memory after their arcs, Simon comes up whenever Jellal plays a key role in an arc, and Ur's fate ends up playing a role in resolving Ultear's story roughly 200 chapters after she was last mentioned.
For the Evulz: Edolas!Erza admits that she hunts people down solely because she likes causing pain.
Fourth Wall Mail Slot: At the end of each volume there's a Q&A corner that Lucy and Mirajane take part of with occasional visits from other characters.
Groin Attack: Lucy goes all out with this one, combining it with Trying to Catch Me Fighting Dirty. She convinces Jose that yes, she is in fact going to use a bucket as a toilet if he's not going to let her use a washroom. Then she winds up and kicks him in the balls from behind in an attempt to escape.
Guns vs. Swords: Erza and Bisca use the same magic and the latter admires the former.
Heel Face Return: When Natsu and his friends return from a mission, they suddenly discover that Gajeel has joined their guild. They are not amused.
Heel Face Turn: Kageyama, Lyon and most of his underlings, Juvia, Shou, Simon, Wally and Miliana, Gajeel, Fried, Laxus, a Nirvana-influenced Hoteye, Jellal, Meldy, Ultear, and the Celestial Spirits Gemini, Caelum, and Capricorn (though the last was possessed by Zoldio). In short, Fairy Tail loves this trope.
Then came chapter 281, it shows that Sabertooth isn't so good after all.
Heroic Fantasy: Fairy Tail as a manga is inspired by European tales of old from various cultures, but is set mostly in a town in the middle of a world fabricated completely by the mangaka where magic is commonplace, and there are parallel universes. Time is measured in centuries that haven't reached 4 digits yet, and yet 20th Century inventions exist, and everyone wears some degree of classical costumes and modern designer clothes for some reason! Swords and sorcery are present in many forms.
Heroic Sacrifice: Ur and Simon. Erza, Juvia, and Lyon all try at some point, but ended up surviving.
Heroic BSOD: Gildarts does this to Natsu (the local Determinator and Idiot Hero) in the last arc by putting the fear in him. That's right, what dozens of obscenely powerful villains, near-death experiences and assorted demons could not do in 200+ chapters, he did it in the span of five panels and he do this by simply getting serious. That how badass Gildarts is. It should be pointed that this is a more benign example than usual, for he does it to help Natsu grow as a wizard.
High Heel Face Turn: Performed mid-battle by Juvia while a member of Phantom Lord. She is one of only two characters who changed guilds at the end of the Phantom Lord arc, the other being Gajeel.
High School AU: The entire premise of the second OVA. All the characters retain their basic personality traits, but they manifest in different ways. (eg. Natsu has Tobasco sauce and hot rocks instead of fire magic, Gray eats snow cones and has his stripping fetish, Lucy uses her cell phone to call in favors from friends). The plot for the second half is essentially a truncated Phantom Lord retelling.
The whole battle with Grimoire Heart is a sequence of these. Gajeel defeating the first arriving Grimoire Heart members, nearly killing himself in the process? These are only scouts, and the real enemy fighting force, the Seven Kin of Purgatory, are far more powerful. Makarov getting serious from the beginning and nearly destroying Grimoire Heart's airship? The airship is restored in seconds and guildmaster Hades steps up to curbstomp Makarov. Fairy Tail members on the island miraculously managing to defeat most of the Seven Kin? Hades' second-in-command, Bluenote, steps in and blows most of those still standing away with no effort. Cana managing to bring the secret magic of Fairy Tail, Fairy Glitter, to bear against Bluenote? It doesn't work because he's just that much more powerful than her. Gildarts, Fried and Bickslow returning to the island and seemingly overpowering Grimoir Heart members for a moment? Azuma seizes control of the island's magic so that instead of protecting Fairy Tail members from death, it instead drains their power. Natsu, with the combined power of his and Laxus' respective elements, proceeding to kick Hades' ass before finally knocking the guy out? Hades gets up without a scratch five minutes later and whips out his strongest magic.
There is another one in chapter 261 with Lucy, Erza, Wendy, Levy and Juvia. Natsu, Gray, Jet and Droy try to do some Outdoor Bath Peeping.
How the Mighty Have Fallen: Fairy Tail completely falls apart after the tragedy of Tenrou Island and is now a nearly defunct guild who can't get any jobs. The few members who remain are haunted by the loss of their friends and are constantly harassed by the town's new dominant guild.
Huge Guy, Tiny Girl: Levy and Gajeel, as partners for the S-Class exam. Levy stands about five feet tall, and Gajeel is tall enough that he can -- and does -- use Levy's head as a convenient elbow rest.
Gray telling Natsu to put a shirt on or Lyon telling Gray to put a shirt on despite not wearing one.
Lyon: Gray, do something about that stripping fetish.
Gray: I don't wanna hear that from you!
I Am Spartacus: After seeing that the Earthland versions of Hughes, Sugarboy, and Coco have no idea what Lucy looks like, Michelle, Natsu, and the other guild members invoke this in order to let Lucy escape safely.
Immortality Inducer: During the Tenrou Island arc, Hades' source of power and life is a device called Devil's Heart. The good guys have one too in the form of the Tenrou tree growing on the sacred island.
Team Natsu (Plus Wendy and even Carla and Lily) charging intoHades' ship while exhausted and with the knowledge that Hades defeated Makarov. They didn't even need to since Hades wasn't going anywhere and his objective (Zeref) was elsewhere. Grabbing Zeref (Gray even knew where he was) and leaving would have been infinitely more intelligent and was never even considered. This is more an example of Honor Before Reason. Perhaps Natsu wouldn't have considered running with Zeref under any circumstances, but he'd be the only one of that group. No, Grimoire Heart had kicked in their door, basically invading their home and trying to kill them all off, on top of successfully destroying the island. It wasn't that they were unable to consider tactics, it was that they were pissed.
Idiot Hero: Natsu's actually a subversion. He's quite intelligent, he's just too impulsive to actually use his brain.
And that actually becomes a key element in his fight against Cobra of Oración Seis. "This can't be...! This guy...! He isn't thinking at all!" To be fair, that was in the heat of battle... and only when he realized he had to, as until and after that point he was continually trying to use cleverer strategies only to have them thwarted via mind reading.
Ignored Enemy: The anime occasionally Lampshades this by cutting to the opponent's nonplussed reaction while the main characters are ignoring them to argue amongst themselves.
I Let You Win: How Cana and Lucy were able to defeat Fried and Bickslow so quickly during the S-Class promotion exam.
Also turns out to be used by Mest in the same event.
Edolas!Lucy does this as well to differentiate herself from Earthland!Lucy, though there's a minor subversion, in that she claims it isn't important because the people in Edolas are too focused on trying to survive instead of their appearance. It's still viewed as an Important Haircut by the others, though.
Edolas!Erza also pulls this stunt for the same reason as Edolas!Lucy. Erza knocking her out, stealing her clothes and impersonating her probably helped in that decision.
Juvia sometimes gets this after misinterpreting one of Gray's comments as a come-on.
Natsu, Happy and Wendy each imagine what Edolas Erza would be like. They're all DEAD WRONG.
Imagine Spotting: Juvia's Imagine Spots are either visible, or everyone just knows her too well. Carla being able to see them is probably due to her having mild psychic powers.
Incendiary Exponent: For Natsu a typical meal is usually something like a chicken leg, a plate of spaghetti, and a drink; only everything is on fire. Even the drink. With regards to the drink, maybe it's not so impossible if we consider one of those flaming cocktails.
Informed Ability: Erza says that Ichiya is a powerful wizard, but thus far he's been beaten up for comic relief, got taken out by a party of nameless thugs, and the only useful ability he shows are perfumes that can act as a painkiller and temporarily boost his strength, both of which have only been used once.
As if to underline this, his stats given for the Grand Magic Games are downright pathetic, leaving him outclassed not only by his own teammates, but by everyone else participating in the tournament.
Intercontinuity Crossover: With Flunk Punk Rumbleof all series (apparently because it's Mashima's favorite series, done by a former assistant). And apparently the author of that series's favorite author is Mashima, so that probably helped things along quite a bit. Most stunning of all is despite the WTF, it ain't half bad. The joint attraction of having both series' voices of reason in the same place being just one hilarious example.
Invisible Jerkass: In a filler episode. Lucy isn't the worst offender out their, but the first thing she does when she reaches Fairy Tail is get everyone to fight one another.
It's All My Fault: Gray does this during the Galuna Island arc. As a child, he set out to defeat the demon Deliora, who had killed his parents. His mentor Ur saved him by sacrificing herself to seal Deliora away. He's lived with the guilt ever since.
↑Though sometimes she tends to take things way too seriously