Continuity mistake: When we see the first instant messaging conversation between Stone, Izzy, and Tim, Tim's screen name is "Tim86". However, when Tim starts talking to Stone, it has changed to "Tim79."
Continuity mistake: As Mercedes flees after cutting the captain, her hair is done up in a braid, but in the next shot her hair is down and flowing. (01:34:05)
Continuity mistake: After Hellboy defeats the semi-vampiric heads, the Professor is seen destroying a small statue on his scroll representing them. Despite being destroyed, this statue reappears later in the movie.
Continuity mistake: Arthur had only 36 hours to spend in the Minimoy world, and he leaves at midnight. He spends a full 24 hours too long as a Minimoy. After he finds the Minimoy Princess they travel during the day. They spend the first night sleeping in a flower (24 hour mark); the second night he is wandering under the house, the grandma is sleeping in a chair above him (48 hour mark). He then returns at noon. That's 60 hours.
Continuity mistake: When the monster puts down Hanso after she tries to escape, you can see her footwear is completely dirty, but in the next shot where the monster's tail uncoils itself from her body, you can now see the pink and white of her footwear that you couldn't see before.
Continuity mistake: At the garden party, when Scarlett Johansson is sitting on the bench and talking, her hair is alternately tucked in and then on the outside of the sideframe of her glasses.
Continuity mistake: Near the end of the film, Violet infiltrates the complex and makes her way into a white room with tons of men in white suits. She starts fighting them and when a couple of guys come at her, she moves quickly and one guy stabs the other in the chest. When she goes to elbow one of the guys in the face, watch his helmet, it comes flying off, revealing his head and hair. When the camera quickly changes to another angle, his helmet is on perfectly straight. (01:17:45)
Continuity mistake: When young Kostya is standing on the table with the jump rope tied round his neck, its knot repeatedly changes position, from Kostya's front to his back.
Continuity mistake: After Stark fights with the Wakandians his armour is damaged, but while he is drinking on the ship the damage is repaired, then the suit is broken back again.
Continuity mistake: When Raven is attacked by the shadow creature in the graveyard, it leaves a number of smears (ink) on her cloak. But as she proceeds to phase through the tombstones in an attempt to shake it off, the smears have vanished.