Zack started joining almost every club at Horace Hyde, and he becomes overworked when he had to attend every club and finish all his projects. When a new mirror enters the school, he discovered that another Zack had entered their dimension from the mirror. Zack Two worked on the projects for all the clubs, while Zack One did the leftovers. Zack Two began signing Zack up for even more clubs, and Spencer and Cam had to try and send Zack Two back, before Zack One had so many things on his schedule that he would kill himself.

Sarah ends her relationship with Zack. Zack discovers a sword in a stone, and pulls it out. Then Merlin appears, who is usually ""an old guy with the blue hat"", is now in the form of a teenager, and reveals that he was trapped in the stone and continued to grow younger instead of older. No one can see Merlin, except for Zack, and no one else could pull out the sword out of the stone except for Zack. Zack decides to ask for getting back together with Sarah, so Merlin grants him his wish if he completes his quest of bravery while Spencer is thrown all around while trying to obtain some evidence of the 2000-year-old wizard.

Zack develops super-human strength to save his father's life. But instead of going back to normal after his adrenaline cools down, Zack gets stronger. So strong he's dangerous!

One minute Cam is making fun of Zack, the next minute he is a frog! Spence and Zack must turn Cam back into a human before Vernon takes his place on the swim team.

When Daniel Greenburg accidentally buys Girl Power deodorant for Zack while shopping, and Zack uses it, he becomes a girl! Now, Vernon is flirting with Zack, while Gwen starts plucking his eyebrows. And even worse for Zack, Cam is going on a date with Sarah. Zack decides to find out how to change back into a boy after he gets some secret information from Gwen and Sarah.

When Spencer was doing an experiment on Zack for his sleeping habits for the science fair, Spence discovers that Zack can enter other people's dreams. Zack fell asleep after Vernon did, so Zack invaded Vernon's dream. The case is that Zack invade other people's dreams when both are sleeping near each other, and as a result, Zack does not sleep well. Zack enters Gwen's dream for Spencer's experiment for the Science Fair and to get tickets for the concert for Cam, Gwen thinks that Zack is ""the man of her dreams"" so the 3 kids have to finds away to help with Zack's problem of lack of sleep.

When Zack and his friends go on a camping trip, Zack's father decides to join them to give them tips. Zack, trying to get away from his father wanders into the woods with Spence and Cam. But they were suddenly zapped into another world, and they must try to find a way out.

When Zack, Cam, and Spence join to figure out more digits after the decimal for pi, they surf the net to check out information about a new rock star. But when Ms. Arlington arrives, and checks what they were doing, Zack lost himself in the bracelet on Arlington's wrist. Then he could not lie and told everything what the boys were doing, and telling the truth to everyone. Cam and Spence must get him back to normal before blabbers out information that would get them into more trouble.

Zack has a record of the lowest mark at Horace Hyde White, producing an F-minus on a physics quiz, so when Spencer downloaded an internet physics tutorial to help Zack's intelligence, Zack's headphones were plugged into the modem, making Zack a genius. Spencer's goal was to win the Physics competition, but when Zack came in, he was even better than Spence at Science. This almost led to a break up of friendship.

Loose Lips: A Dog's Story When Zack accidentally learns the secret to communicating with dogs, but he only can communicate with them if the dog is in a moving vehicle. No one believed his story, but a dog spoke to him and told him there was an impending bomb threat. This bulldog named Spike was a former police dog which sniffed out bombs.

Zack creates a comic book about his ears, because he did not like everyone saying that he had big ears. It turns out that Zack destroys the comic and everyone thinks that it was about Zack and Sarah, so Vernon goes to repair it and humiliated Zack by presenting in front of a large audience.

While Zack along with his classmates, visited the museum for a school trip, Zack touched a field phone which gave him shell shock, just like a soldier who had also used a phone in World War I. Now, whenever Zack is exposed to an old object, his personality transforms into the owner of the object. Spencer and Cam must find a way to reverse the effect before Zack touches an object that did not have an owner or existed before the Holocene Period, where humans were not alive yet.

A boy named Gilbert, has come back to finish unfinished business when he was alive. And now, Zack is the only one who can see him, so Zack is being blamed for all the pranks Gilbert is setting up. Pranks are pulled all over Zack's house and the entire school. Zack, Spencer, and Cam must find out what Gilbert wants before he gets Zack expelled, kicked out by his father, or being killed.

Anchovy of Doom When he was working on his science project about Human Apportion, Zack decided to take a break and eat some pizza, but before he ate, he zapped Gwen, Dickie, Tad, Todd, and Vernon into a terrarium and all of those 5 became only 8 centimetres tall.

Zack wanted to stay and work on his project with Spencer and Cam, so he tried to trick Floyd, by turning the clock handles back to a certain time but they were transported into the past where they meet a boy. When they returned to their own time, the boy from the past came with them. So now, Zack, Spencer, and Cam has to return the kid back to his time before it's too late.

You Don't Say Zack and his Dad pay a visit to Henry Gold's Magic Shop where Zack picks up a guide to Vaudeville ventriloquism. With a little practice, Zack learns to throw his voice. He started to have some fun during class, and humiliate Vernon during his presentation, etc... Soon, Zack's voice was becoming more weak and Zack was starting to lose his voice. Suddenly, his voice was released from Zack and it starts telling everyone his secrets. Secrets about his friends, and Zack must retrieve his voice before all his thoughts about his friends are out.

It's a Wonderful School It's election-time at Horace Hyde-White School for Boys and Headmaster Killerby unveils his latest acquisition - an early 20th century voting machine. Everyone's worst nightmare is realized when the voting machine misfires, transforming Horace Hyde-White into the Vernon Manteuffel School.

Quiet Please, I'm Reading Your Mind It's hard to mind your own business when you're suddenly given the power to read other people's minds. While embarking on some surveillance, Zack is zapped by a headset, leaving him with the temporary ability to read other people's minds.