Caution: Unmarked spoilers ahead!
James Wan is a horror movie veteran who went out of his way to instill terror into the first Aquaman movie, so it should come as no surprise that he'd crank up things for the sequel.
Film
- Black Manta's rage and hatred of Aquaman drives him to become The Dreaded and aim to destroy everything Arthur cares about: his home, his kingdom, his family. He doesn't care what he has to do to enable it, whether it's killing children or ravaging the world itself.
- While exploring Antarctica, one of Dr. Shin's associates is attacked by some...thing. We don't get to see what it was beyond a tentacle with fingers.
- Black Manta plans to release Kordax with the blood of the Atlantean royal family. Orm assumes he's coming after Arthur and himself, but Arthur reveals that they're not the last in their bloodline - his son is, and Black Manta has kidnapped him! This is directly based on the comics storyline where Manta murdered Aquaman's son, an event that affected the hero for decades. Thankfully the film averts this, with the baby eventually rescued.
- Kordax is Atlan's brother who ruled over Necrus, but the continued use of oricalchum began to affect his mind, also causing the global temperature to rise and endanger the world. Kordax for his part was driven mad and became paranoid towards his brother, later transforming his people into horrific tentacled zombie creatures and turning his kingdom into a dark industrial site filled with monsters that are poisoned beyond recovery. Kordax's final appearance is as some kind of lich king, corrupted so much by oricalchum that he became inhuman - his trident enables him to possess anyone who wields it... but the members of his bloodline are the most vulnerable.
- When Dr. Shin stands up to Black Manta, the latter pulls his knife on the doctor and states that he only unsheathes it when he plans to draw blood. True to his word, a drop of Dr. Shin's blood can be seen on the blade as he pulls away.
