Luffy's first and second consecutive defeats by Crocodile. The only Straw Hat at that point in the story to be severely beaten was Zoro (by Mihawk), so naturally the main character being handed two defeats in a row out of nowhere (and by being impaled by an enormous hook hand and then dried out into a skin-sack, no less) was pretty surprising for the audience and the crew (This also marks the first in a long series of epic battles where Luffy pushes himself to the extreme for his friends; a trait that eventually nearly costs him his life hundreds of chapters later).
The Straw Hats getting curb-stomped by Aokiji at Long Ring Long Land, even as they all teamed up against him, showed that there were characters vastly stronger than any of the main characters. This incident provoked Luffy into finding new ways to get stronger, now that he was aware of people like Aokiji.
Water 7. The lovable and helpful square-nosed carpenter, the hilarious and Bad Ass ventriloquist, the sexy secretary, and the kindly bar owner? Yeah, they're the villains.
And that's relatively tame compared to the other plot points : the Going Merry is revealed to be damaged beyong repair, Robin leaves the crew for then unknown reasons and supposedly betrays the crew, and Usopp, due to both his own fears of being too weak and Luffy's decision to get another ship, not only leaves the crew as well but also challenges Luffy for the ownership of the Going Merry. Holy shit. Long before Marineford, Water 7 was also a Wham Arc.
Nearing the end of the Enies Lobby Arc the Straw Hats are visited by a high ranking Marine, then the identities of Luffy's father and grandfather are revealed. And nobody saw that coming.
The explosive end of the Sabaody Arc, leading to the events of chapter 513. Quite possibly the greatest Wham in the entire series simply due to how it was delivered; After teleporting Zoro away in the last chapter, Kuma goes on to single-handedly deliver the entire crew their first true defeat (as a team) by teleporting every single last crewmate to several different locations across the globe. And mind you, this was literally right before they were about set sail for the New World. With NO hint by Oda AT ALL that any such thing was about to happen, this left the entire fanbase stunned as the next 88 chapters were focused solely on Luffy's adventures. Jaws were dropped, tears were shed.
The anime extended the scene, added in a reverse Nakamania montage set to a violin solo version of Binks' Sake, and to increase the impact for the Anime only crowd followed the scene with a alternate universe filler arc so that you didn't find out what happened to everybody for another few weeks!
Not to mention a display of Bartholomew Kuma's sheer power—his bounty is lower than Gekko Moriah's, whom Luffy had recently defeated, and Luffy had grown much stronger since fighting Aokiji, but Kuma curb-stomps all of the Straw Hats just as easily as Aokiji did before. This time, however, all of the crewmates saw each other vanishing into thin air, and the chapter ended with the declaration of the Straw Hat Pirates' eradication. It was painfully obvious the series was taking a different and darker direction at that very point.
The entire Whitebeard War arc can be summarized as a progression of Wham Episodes, each more shocking than the last:
First of all, Ace being revealed as the son of the late Pirate King, Gold Roger.
It really is a big one, considering that there was no indication that Gold Roger had a lover, let alone a child.
Chapter 573. Admiral Akainu punches a hole through Ace's chest with a magma fist. The name of Chapter 574? "Portgas D. Ace Is Dead".
Okay, so things can't possibly get any worse now. WRONG!!! Right after Ace dies, Whitebeard orders his men to take Luffy and escape while he makes his last stand against the Marines. After Akainu blows off half of Whitebeard's face, Blackbeard suddenly shows up with his crew and the most dangerous prisoners from Impel Down. After a brief one-sided fight in Whitebeard's favor, the rest of Blackbeard's crew retaliates with a joint attack, finally killing the old man. After which, Blackbeard does... something while hidden away from anyone else's view, he comes back and reveals that he's now taken Whitebeard's earthquake powers on top of his own darkness-based powers, something that's supposed to be impossible, and proclaims that the new era now belongs to HIM.One Piece might go from being a Crapsaccharine World to just a Crapsack World. Marineford is THE Wham ARC!
Let's continue that trend, shall we? Chapter 579 achieves a Crowning Moment of Awesome as the pathetic wimp Coby finally snaps under the pressure and shouts at the top of his lungs that all the fighting between the pirates and marines was pointless. This effectively causes ALL OF MARINEFORD to stop fighting to listen in. Coby shouts how continuing this fight no longer means anything. All the pirates and marines who have lost their lives in the senseless fighting would only look like complete idiots in the long run. The Marines had accomplished their goal of killing Ace, but now they insist on fighting off pirates who don't want to fight back, and just extending the battle beyond what it needs to be. He doesn't care if he gets punished by the Marines for his outburst, but he does it anyway. Unfortunately. the Marines insist on fighting further... Then Shanks shows up to put an end to this war.
The end of the Fishman Island arc drops a whole bunch of plot points one after the other:
Shirahoshi is the Ancient Weapon Poseidon.
Aokiji and Akainu fought for 10 days over who would become the new fleet admiral, with Akainu being the victor.
Blackbeard has become one of the Four Emperors and is looking to hunt down powerful Devil Fruit users to take their abilities.
And finally, Luffy has challenged Big Mom over ownership of Fishman Island.
The Punk Hazard gives us:
Trafalgar Law is a Warlord.
The production of fake devil fruits.
With the deaths of Monet and Vergo, Ace and Whitebeard were not a one-time example, from now on, named characters can die outside of flashbacks.
Chapter 700: The latest roster of the Shichibukai is revealed, including Buggy the Clown, and Doflamingo has Ace's Flame Flame fruit.
Doflamingo never stepped down from being a Shichibukai. That is all.
Remember when Doflamingo claimed that he was only a warlord for kicks and that he could quit any time he feels like it? Turns out the reason he's not scared of the consequences of this (facing the admirals) is because he's actually a world noble, and can overrule the marines if he wants to, which is how he pulled it off.
Chapter 718 reveals the conflict between the Dwarves of Tontatta Kingdom and the Doflamingo Family began not 10 years ago when Donquixote Doflamigno took over Dressrosa, but over 900 years ago, at the start of the Void Century.
Chapter 722 reveals that out of the 20 founding Kingdoms of the World Government who live in Mariejois, only the Nefertari family (Vivi's family) refused to join; the rest became the Celestial Dragons, while their own nations would create monarchies to replace the lost families. The monarchy that the Riku family (Rebecca's family) replaced was the Donquixote family.
Chapter 726 confirms that the man in the knight helmet is in fact King Riku and that Thunderous Soldier of Rage is Rebecca's biological father.
Chapter 728 reveals that Violet's true name is Viola, the daughter of King Riku, making her Rebecca's aunt and Scarlet's sister or sister-in-law. Her devil fruit abilities interested him enough for her to make a deal: she would subject herself to service to the Donquixote family in exchange for her father's life.
Chapter 729, just as the Straw Hats are gaining the resolve to defeat Doflamingo, he shows up, having defeated Law, but ups the ante by shooting him three times.
Chapter 730: The Straw Hats already have their hands full with Doflamingo kidnapping Law after injuring him in the last chapter, but the Thousand Sunny group encounters one more problem: one of Big Mom's ships coming to get Caesar.