Having evil, same looking relatives is common on magical themed shows. The television show Bewitched features an evil cousin, as does I Dream of Jeannie. Also, the stars of each respective show played their evil relative.
In "Sabrina and the Beast", Cousin Susie gives Sabrina a whip (one of the clues), and also adds 'We all have good and bad parts'. In this episode we find out what she meant - but that was still not a direct clue to the board's family secret. The board just mentions a twin, and Sabrina only later finds out (when the aunts tell her directly) that one of the two is evil.
Sabrina gets her Witch's Licence in this episode.
In this episode, Sabrina figures out that the family secret is "Every member of the Spellman family is born with a twin."
In this episode, Sabrina learns that lava is the only substance that can destroy a witch.
Running Gag: Zelda being forced to eat sand while Hilda happily cheers on.
Turning Libby into pineapple was an accident and so shouldn't have been included on the video.
Near the end of the episode where Sabrina is back home and the cat has had kittens. The kittens in the box look more like baby rabbits than kittens, they have long floppy ears that if I'm not mistaken aren't associated with kittens.
Sabrina's evil twin is shown helping mortals with her magic; she helps a handicapped man walk, and rebuilds a little girl's sand castle, and the Witches' Council applauds her for it! In reality, the Witches' Council should have punished Katrina for her actions, since all the things she did were examples of CHARITABLE magic. In season one's "Terrible Things," it was stated that witches' were not allowed to help mortals by using their magic.
When the video clips from previous episodes are played, one of them shows her using magic to make Mr. Kraft's pants fall down. This was one of the bad things Sabrina had supposedly done using magic, however she was actually under a spell then and had Libby's personality, so technically it wasn't actually Sabrina's personality who had done the bad deed.
Pele: Well here it is, your official witches' licence. It will give you more power than you ever dreamed possible.
Zelda: But be careful, it can also cause more trouble than you ever dreamed possible. Just ask Hilda.
Hilda: Not all tsunamis are bad.
Witch Judge: No good witch has ever had the heart to do away with their evil twin... although one Hilda Spellman did come very close.
Zelda: Evil twins are thrown into the volcano.
Sabrina: Oh, to prove that they're brave and then they'll be welcomed back into the bossom of their family?
Sabrina: Why are we at a volcano? I thought I just couldn't live in the mortal realm.
Zelda: Well actually dear, you can't live in the mortal realm or the other realm.
Hilda: We didn't want to worry you and besides, I never thought you'd turn out to be the evil one.
Zelda (to Hilda): Especially when you turned out to be the good one.
Sabrina: Well, I'm a wreck.
Zelda Oh calm down, dear. Just because your spell was selfish.
Hilda: And involved civil disobedience.
Zelda: And was very messy, doesn't mean you're the evil twin.
Witch Judge: Order on the sand! Since Sabrina's 'helping a pregnant cat' spell was selfish, involved civil disobedience and was extremely messy, the evil twin is... Sabrina Spellman!
Sabrina: Great! I finally win something...
Salem: Looks like Inexact Spell Spellman has struck again.
Sabrina: I'm good, I know I am. Or am I? Wonder if there's a competent therapist on this island?
Witch Judge: Court's adjourned! The last one to limbo is a rotten egg!
Harvey: I got this scar wrestling a monkey at the county fair.
Salem: Sweet! But I got you beat. Check out the one on my butt.
Harvey: I don't see a scar.
Salem: Don't have one, but made you look!
Zelda: In all witch twins, one twin is evil and the other one is good and, unfortunately, the evil twin is not allowed to live in the mortal realm.
Sabrina: Oh no! Katrina can't be the evil one! Wait a minute, that would mean I'm the evil one. She did leave the pool boy a crummy tip.
Katrina: Hello Sabrina.
Sabrina Wow! I'm so excited... and apparently not unique.
Zelda: Hilda, at the last family reunion you managed to alienate everyone because you hadn't even read the family newsletter.
Hilda: Oh it wasn't that bad!
Zelda: They made you eat sand.
Hilda: Not a lot.
Sabrina: Well I'll just call room service and er... ponder over this, while I have a burger and some free movies.
Hilda: Sorry, no food, no fun.
Zelda: You have to work on it until you get the answer.
Sabrina: I just want to thank you two for bringing me to Hawaii.
Zelda: Hello Harvey, this is Lola.
Hilda: She mostly just wants to be left alone.
Harvey: An excellent quality in a pregnant thing.
Salem: You got a mortal to stay with us? So what if I need something for Lola? How am I supposed to let him know? Charades? Come hither stares?
Sabrina: What if I put a Doctor Doolittle spell on Harvey? That way you two can talk to each other.
Salem: You've done that spell before?
Sabrina: No, but I can. I discovered it while studying the magic book.
Salem: Studying the magic book? Who are you and what have you done with Sabrina?
Harvey: My dad's away and according to my mom, pregnant women need soy hot cocoa brought to them every half hour throughout the night.
Sabrina: Well are you sure your mom's pregnant and not just lazy?
Harvey: I need a break. I'm thinking about joining the army.
Hilda: The bad news is we're going to a family reunion.
Zelda: The good news is...
Sabrina (interrupting): It's not our family?
Sabrina: Can Salem come visit every other weekend?
Harvey: Sure, that way we can watch Robocop together... Why did I say that?
Sabrina: I have to get rid of that Doctor Doolittle spell.
Salem: Why? Just because you're evil doesn't mean I shouldn't continue my friendship with Harvey.
Sabrina: Hi Harvey.
Harvey: Aren't you supposed to be in Hawaii?... Without a moustache?
Hilda: Sand goes down better the second time, don't you think?
Zelda: I understand your not stopping them but did you have to scream out "More! More! She can take it!"?
This episode contains about two minutes of clips from previous episodes.
The character called Pele says she is the Hawaiian goddess of fire. This is based on a real Hawaiian story. The goddess Pelee can turn into a firebird and fly over the volcanoes. She considers lava rocks to be her children and if people like tourists take them, they will be cursed. This is also a possible reference to Mt. Pélée, a volcano in the Caribbean.
Sabrina: Get me the ACLU!
This is a reference to the American Civil Liberties Union which works to protect American's original civil rights.
The episode title, "The Good, The Bad and the Luau," is a possible reference to the title of the classic western movie, "The Good, The Bad and the Ugly."