The Zack Files - Season 2 Episode 17 Zack Times Two

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.