Kai- loosing his powers. He is almost willing to do anything if he gets to keep his beloved powers. Otherwise he feels like he is just average. Also water.

Zane- loosing Pixal. When he fears that Pixal is dead or in trouble, he puts aside all other priorities and focuses on her.

Cole- Dragons? No. Snakes? No. Ghosts? No. Well then what is he afraid of? Idk... let's just say no cake and move on.

Lloyd- being evil. He doesn't want to be like his dad.

Jay- Nya cheating on him. After she cheated on him with Cole, it has always been his worst fear that one of his friends may take Nya away from him.

Nya- failing. As shown in season 5, Nya is amazing at so many things but when she fails, she gives up.

Pixal- loosing the ones who are most important to her. She would be deeply upset if she lost someone like Nya but she would feel broken if Zane or Borg died.

Wu- Jigsaw. I don't even have to explain this.