The role of Merle's father (Walter Brocken) was played by James Doohan, who is best known for his role as Scott on Star Trek (1966), starting the following year. Craig Huxley, who played Merle, guest starred in two episodes of Star Trek (1966) - Operation -- Annihilate! (1967) & And the Children Shall Lead (1968).
Anne Sargent plays a witch named Margaret Brocken, breaking with an unspoken tradition of ending all witch's names with the letter "A": Samantha, Endora, Clara, Enchantra, Hagatha, Grimalda, Esmeralda, Serena and Tabitha.
Walter and Margaret Brocken take their surname from Mt. Brocken, also called the Blocksberg, the highest peak in Northern Germany. It's the traditional legendary site of annual witches' Sabbaths, a bit of folklore that Goethe used in his play Faust.
When Darrin drops a 50-cent coin in the bar, a stranger attempts to steal it. To put that in context, back in 1965, 50 cents was worth almost five dollars in 2022 money.
The young actor who played the boy warlock in this episode (Craig Huxley) also played Captain Kirk's nephew, Peter Kirk, in the original Star Trek (1966) episode Operation -- Annihilate! (1967).