I've heard of "scariest" as a superlative form of the adjective "scary". But, I'm not sure about "scarediest". Is it a common phrase in the U.S.?

Why's she talking about "red carpet?"

She is referring to the long red carpet laid on the ground for special guests to walk on when arriving at an event or place. It's commonly associated with Hollywood events. It's mentioned here because she is saying that these types of events often begin during the daytime, out in the open. Ex: The supermodel walked the red carpet at the Met Gala. Ex: I had a red carpet for my wedding guests. It made them feel special.

Can I use “couples of”, not “a couple of”?

No, saying "couples of" changes the meaning of the original phrase. "A couple of" refers to 2, while "couples of" refers to multiples of 2.

What does "spoiler" mean? Does it somewhat related with the word "spoil?"

Yes, that's right! Especially in the literature or film context, a spoiler is a description of an important plot development that may affect or ruin the experience of the book or movie (it "spoils" it). For example, if your friend tells you about what will happen at the end of the book you are reading, that is called a "spoiler." Ex: Be aware that if you google things about movies or books online, there may be spoilers. Ex: I hate when people spoil the plot of something. It ruins the experience for me.

What is the role of "a couple of" here? How different are "break a couple of rules" and "break rules"?

"A couple" means more than two, or a few. When used in this context, it works to add a rough estimate of numbers: a couple, a few. The speaker has used "broke a couple of rules" to add a feeling of casualness to the statement. "Break rules" sounds a bit too stiff, so using a number-related expression like "a couple," "a few," or "some" can be used to make the sentence flow more smoothly and sound more natural. Ex: Let's buy a couple bottles of wine and stay in tonight. Ex: I have a couple errands to run today, so I won't have time to hang out with you.

Just curiosity, but in what circumstances can I use the word "wacky"? Can you show me some exemplary sentences?

"Wacky" is used to mean that something is amusing or funny in a strange way, so it is comparable to the synonyms "crazy," "quirky," "outlandish," or "eccentric." Ex: The movie was overall quite wacky and nonsensical, but it did have some moving moments. Ex: The man was known for being wacky. He decorated the outside of his house with strange dolls and toys.