When Justin was trapped in the quicksand, his left arm goes under and gets his sleeve all dirty. In another quick shot, his arm is above the dirt and the sleeve is clean. The next shot, his arm is submerged and the sleeve is dirty again.
During the Wizard Competition, Alex had created the first mud puddle for Justin to fall in and while he was digging around for his wand while she does the floating on water spell. When he finds his he shoots some magic at her. With the camera in the magic's point of view you can see a second mud puddle right next to the Big Magic (it's to the right of the table the ball of magic is on).
Justin changes sides on the wind surf before he runs into Alex.
When Max takes the balloon and blows it up for Archie using magic he takes it into his right hand. But when he blows using magic it up it appears in his left hand. Then when they show an angle from behind Max the balloon is in his right hand again. Then when Max hands the balloon to Archie it is in his left hand.
When Justin crashes into Alex the line of shade is about even with the sand castle. But when she lands on the sand castle the shade line is past Justin who is a ways back from the sand castle.