Question: Does Salem ever become human again?
Chosen answer: No. In the show he was sentenced to 100 years as a cat and only served 25 years at the time of the pilot (all episodes of him being human are flashbacks). The comics did several retcons to change Salem's backstory to fit the show's, and as of 2015, he was still a cat.
Instrument of Destruction - S1-E12
Question: Throughout the entire Power Rangers series, Skull has shown to scream in fear whenever confronted by a terrifying monster or a group of them. In this episode, how was Skull, who was dressed up as the Phantom Pianist at the time, able to keep his fear in check when the Cogs came to get him?
Answer: Instrument of Destruction.
The question was how was Skull able to keep his fear in check when the Cogs came to get him. Not what episode it happened in.
Arnold's Hat/Stoop Kid - S1-E3
Question: Did Harold already know that the Stoop Kid had just left his stoop the first time? He would have known that a while ago due to a large crowd in the city or even in the newspaper.
Answer: No, he did not. He is seen getting off the bus with a suitcase, so he must have not been home for a few days so there is no way he could have known.
Housesitter - S3-E13
Question: Why did Chris cover the faces of his mother on any pictures?
Answer: In the S6 E18, "I, Busybody" Salem got permission from the Witch's Council to be human for one day to meet his pen pal, Roxie. It was all a point of view camera shot.