Episode 336 is Dungeons and Dragons (1983)

A group of kids are thrown into a fantasy world where they must search for a way home, armed with magic weapons that an evil tyrant wants

"The Night of No Tomorrow"

The pupils seek out and find Merlin, and he'll teach the pupil Presto magic, if he stays with Merlin. Presto decides to stay and attempts a spell to create a way home, but the spell summons dragons instead which attack a nearby village