Once and Future Zack - S2.E15

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.