Continuity mistake: Near the end, during the final combat scene between Aquaman and King Orm, the gigantic whirling propeller blades in the background noticeably change rotation rate: At the start of the battle, the blades are turning rather lazily; but at the height of the battle, the blades are spinning rapidly, a virtual blur in close-up shots, drawing a steady stream of sparks from Orm's helmet when it touches the propeller. When Aquaman defeats Orm moments later (and their mother, Queen Atlanna, appears), the huge blades are spinning slowly again. I'm not talking about during dramatic slo-mo action effects, but during the normal-speed action. (02:04:50 - 02:07:10)
Continuity mistake: After Arthur puts his father in the truck after the bar, we see Mera emerging from the water from the left of screen, right of the truck, off to the side casually walking up. When the camera changes we hear a splash and suddenly Mera is on the dock behind the truck dripping water. This is showing that she was walking up from the side, suddenly went back into the water, only to jump back out again at a different spot on the dock.