JoJo's Bizarre Adventure / Shocking

All spoilers are unmarked. You Have Been Warned.

Phantom Blood:

This part starts off as a seemingly normal Victorian-era period drama with elements of horror. But then... Dio turns himself into a vampire and Jonathan must train to use a special martial art known as Hamon in order to defeat zombies.
The final episode, if the title didn't clue you in ^note. With Jonathan having married Erina and set of on a honeymoon cruise with her, you may expect a One Piece style adventure from here on out, since the series is named JoJo's Bizarre Adventure, right? Dead wrong. Dio appears on the ship without a body, fatally shoots Jonathan in the neck with Eye Beams, sends zombies to kill everyone on the ship, and finally, has his Grand Theft Me plans foiled by Jonathan himself, who blows up the ship and dies holding Dio's head in his arms. Erina can only get away in a coffin with an orphaned baby from the ship, declaring her pregnancy and vow to remember Jonathan's story. In conclusion, a very quick way to establish the main story as a generational saga.

This is the point where the franchise begins embracing its own absurdity. It's a globe-trotting adventure in the spirit of Indiana Jones that involves cyborg Nazis, ancient Aztec vampires, and to top it all off the main villain tops Dio by becoming the Ultimate Lifeform.

During Jotaro and DIO's fight, it escalates into near-DBZ tier when both of them start flying, but what tops the "Holy Shit" cake is when DIO drops a motherfucking STEAMROLLER onto Jotaro.
In Episode 47 of the anime, the intro changes to have DIO and The World interrupt near the end, stop time, and then going into a punching duel with Star Platinum, complete with their signature Kiai.

Right after Rohan's introduction we're introduced to Reimi Sugimoto who is the ghost of a teenage girl killed by a serial killer 16 years prior to the story. While the beginning made Diamond is Unbreakable out to be another Stand of the Week-style narrative, here it becomes apparent that the part is an all-out game of cat and mouse between the protagonists and the enigmatic Yoshikage Kira.
The opening of Episode 36 of Diamond is Unbreakable has Kira using Bites the Dust to rewind the opening!

Here, it's even more apparent than in other parts. Almost every Stand in this part takes about two pages to explain how it works, and are ridiculously overpowered. In the case of Epitaph we're not even given explanation of how it works other than.. it just does. Gets even crazier in the final battle where Polnareff awakening to Silver Chariot Requiem causes the protagonists to switch bodies and the world around them to crumble, and Giorno awakens to a Requiem Stand and by that point... good luck understanding the story.

The entire sequence where Heavy Weather transforms people into Snails.
The ending where most of the protagonists are killed off, immediately before the entire universe resets.

During the fight against Civil War, Jesus Christ himself shows up to give Johnny some pointers.

This part still manages to pull this off even though it's more drama-focused than previous ones. Really kicks in when it's revealed that Josuke is a fusion of Josefumi and Kira.
After Chapter 93 and 94 seems to build up for Yasuho to get Killed Off for Real before ending with a two-month hiatus, Chapter 95 reveals that it's not Yasuho who gets killed off. It's Norisuke.
And then chapter 96 reveals that Norisuke is Not Quite Dead, only for chapter 97 to have the Head Doctor seemingly kill Jobin.
Chapter 99 brings out a revelation no one would have expected with the appearance of the Stone Mask AND the Stand Arrows, alongside Lucy Steel mentioning the Devil Palms and the Ground of Morioh, implying all hold similar power considering they are all related to stone or earth in some way.

The series as a whole is one that subscribes pretty heavily to Drugs Are Bad, as is typical of Japanese culture. So it is very shocking when the first chapter immediately has the main character (a deliberately Expy of Giorno no less) be introduced as an underage drug mule who sells his wares to other teenagers and enjoys it, no less.