WMG / Sabrina: The Animated Series

Pi is actually a female pop star disguised as a boy who wanted to escape the constant adoration of his/her fans and live a peaceful life.

Hilda and Salem were lovers once when he was a human.
From what we've seen Hilda really gets around and Salem would have wanted her at some point.

Pi is actually a trans boy and who's gay AND he has a crush on Harvey.
What's more Harvey (and Chloe) know everything and Harvey feels the same way about Pi. Too bad they won't tell the other one how they feel (for now)... Sabrina is out of the loop however and since we see things from her POV we supposedly know nothing as well. But we do.
  • Or Pi could be a cis boy who is in touch with his feminine side. He still could be gay for Harvey though.
  • Pi being attracted to Harvey is so obvious it shouldn't even be WMG

Neither Sabrina or Gem actually have feelings for Harvey.
It's just part of their rivalry. They both think the other one wants him so they fight. Actually they don't really care that much for him.
  • Well then, Pi gets Harvey all for himself! Yay!
  • Too bad he dies

Futura is a witch.
Futura sounds like a mystical enough name for a witch

Zelda was dating Tim
And there's a total bitterness between them now

Salem's human form in Secret life is a younger version of his true form
Well it could be

Sabrina is turning evil
Cassandra didn't Heel-face turn Sabrina did a Face-heel turn but it looked like the opposite way around. Taking into account, Sabrina's more nasty attitude in Secret life this seems possible. Maybe losing Chloe pushed her over the edge

Pi knows Sabrina's a witch
He just doesn't care. He was suspicious of her since Paranormal Pi, started following her and discovered the truth, wrote it in his diary or something and moved on.
http://tvtropes.org/pmwiki/pmwiki.php/WMG/SabrinaTheAnimatedSeries