Villains don't get much more threatening than Doflamingo. Not only did we watch him take out Oars Jr. at the Paramount War with ease, he has mastery of all forms of Haki. He's even got an Awakened Devil Fruit and has the entire Beast Pirates at his back just in case anyone tries to interfere with his plans.

Yet, what truly makes him so menacing doesn't come from his strength or allies, but his history. Being torn away from Mariejois puts his ambitions in an entirely new light. He has the same desire to treat everyone as dirt like the Tenryuubito, but actually has the strength to back it up. It drives home just how truly messed up the world government is that someone as mad as Doflamingo can run free just due to what secrets he knows about the world thanks to his heritage.

It's hard to explain what makes this one so impactful because, at the time, it was a random moment with a strange old man encouraging Luffy to follow his dreams. Even when it was revealed that he was called Blackbeard and that he was chasing Luffy, it didn't have that much of an effect. There was no indication for the role Blackbeard was going to play in One Piece, so he may as well have been the villain for the next arc.

That's what makes this one so good: it's a twist that actually gets better in retrospect. This isn't just anyone giving One Piece’s most inspiring speech in a series known for grandstanding. No, this is the man who would eventually become the main villain of the franchise.

Remember when Vivi was actually a villain? When she was first introduced, Vivi was only known as Ms. Wednesday and acted alongside Mr. 9 as a recurring thorn in the Strawhats side. It was only at Whiskey Peak where she revealed that she was the princess of Alabasta working to infiltrate Baroque Works to stop Sir Crocodile.

This twist is important to One Piece because it set up the scale of the conflicts that the Strawhats would be dealing with throughout the series. No longer are they dealing with corrupt local officials and pirates. Now they were up against a Shichibukai for the fate of an entire nation!

Who would have thought that over 15 years into One Piece there could still be such a massive revelation regarding the backstory of one of its main characters? Yet that's exactly what happened with Sanji, where we found out that he's been a crown prince estranged from his family all this time and no one’s been the wiser.

What especially makes this twist work is how effortlessly it was hidden from the audience, yet all the pieces were there. Since everyone barring Luffy generally only gets one backstory, we thought we knew everything important there was to know about him. No one thought twice about the implications of Sanji not getting a real photo for his wanted poster because, c'mon, One Piece is known for dumb jokes like that. But all that time it was just misdirection so no one would think about Sanji's past.

We've all heard the jokes. "Characters don't die in One Piece". "Only parents in flashbacks can die". "Looking forward to seeing how Oda can justify how someone can survive getting impaled". And so forth. During the first half of the series, no one ever imagined a single major character dying. The closest we got was the (admittedly heartbreaking) burning of the Going Merry.

Those jokes stopped as soon as Ace got Akainu's entire fist shoved through his chest. After that, One Piece suddenly grew up. No longer is the world of One Piece just manga Disneyland, but one where a moment of weakness can lead to irreversible consequences. Remember that time Pell survived a bomb to the face? Or how about when Conis’ father took one of Enel’s thunderbolts at full blast? At the time those moments seemed silly, but now with death a regular occurrence in One Piece, it seems clear now that they only survived so Ace’s death would be more shocking.