Revealing mistake: In the opening scenes, we see a very pregnant Draka reclining on a bed of animal hides as Durotan watches over her. In the extreme closeup, we see Draka twitch her lips, and her small tusks flex from side-to-side with her lips, instead of remaining firmly aligned with her jaw as they should.
Continuity mistake: The crew arrived at the volcanic island in turmoil, and are talking with the local captain. The captain asks them to carry also some of the dead people, and they start asking him what the plan is, if there's one at all. The pass at the neck of the captain shows the side with the symbol in one shot, the blank one in the next. (00:25:10)
Continuity mistake: While Jax is held against the wall by two of the Furies it shows her bare feet held off the ground. As she moves across to Sinbad after he plunges the sword into the third Fury she is wearing flip-flops. (00:29:17 - 00:29:54)
Revealing mistake: When Gabby and Fin are hanging off the building in Las Vegas, you can see that Gabby isn't holding on to anything in some close-up shots. (00:11:47)
Continuity mistake: The sun angle changes several times during the chase sequence when the dragon is on the flatbed truck.
Continuity mistake: After their fight with the monkey Sara has some scratches on her forehead and cheekbone but when she gets to the castle with Freya they are gone.