The Nostalgia Chick/WMG

The "evil storyline" will feature the Chick facing her Evil Twin.

 * And according to Nella's "signs of evil" lesson in "NChick Labs", Dark NChick will have red hair, a British accent and a leather outfit.
 * Won't that make it pretty obvious that she's the bad one? My - most likely wrong - theory is that Evil!Chick will be a lot like the usual Chick to integrate herself, but will be a little too cruel and a bit more violent (especially if the "Ferngully II" review is involved, because 1) no way that it won't be a Critic/Chick crossover and 2) they can never resist fighting) so we would know, but her friends won't realize until its too late.
 * Evil Chick has already taken over the series as of "Disney vs. Dreamworks". That's why she was nastier than usual to Nella and told her "Begone, minion!" That's a definite villain phrase.

One of Team NChick will make a Face Heel Turn.

 * Probably Elisa (The Makeover Fairy). It seems somehow plausible, and Nella is too obvious a choice.
 * Judging by this tweet from Lindsay: "@Nellachronism is putting dents in my cold, cold heart by how Woobie she is in this episode. #woobiedestroyerofworlds" It looks like Nella will snap from all the abuse. Hell yeah.
 * Because of all the abuse, Nella will turn into the anthromorphic representation of the It's a small word ride and trigger the end of the world. Hell, yeah.

The upcoming storyline will tie into the storylines of Atop the Fourth Wall, The Spoony Experiment, and The third year anniversary.

 * The best hope they have of one-upping Kickassia is by creating a site-wide plot that gets 3-4 months of set-up, and this is a perfect opportunity.
 * Especially since SpooningWith!Spoony is at least partly an NChick creation. And Spoony has on one occasion implied that Nella is next.
 * This will cause Nella to stop being the Chick's Morality Chain, with terrible consequences.

All of Team NChick turn evil, and the Chick leads them to depose the Critic in a coup.

 * The Chick seizes control of TGWTG.com, and even the site's logos change to reflect it. Either she becomes Drunk with Power and everyone chafes under her rule, or she discovers that corralling the other contributors is a huge pain that threatens to drive her mad.
 * The MacGuffin will be The Nostalgia Critic's hat; wearing it signifies rule of Channel Awesome.

Now that Nella is gone, Chick will snap and get even worse.

 * The only way for her to come back from pure evil is through a MacGuffin that will bring Nella back to life.

The Chick will make a whole video dedicated to Stuffed Into the Fridge

 * For craps sake, she was literally just stuffed into one.

The result of the storyline will be that the Chick becomes more open.

 * Lindsay said the arc will involve a bit of Character Development, the Chick has been told twice she has to unleash her inner fangirl and she's expressed regret that she didn't tell Nella that she was sometimes a wee bit more than her beleaguered bitch, even in other episodes it's hurt her to say something is actually properly good and she's had to stop from being angry/too emotional a few times and made herself go back to analysis. She won't change much, just not be so stoic.
 * Confirmed at least in part by the X-Men commentary.
 * Although jossed. She's still the Lack of Empathy sociopath we know and love.

Dark Nella will be defeated by the MacGuffin that Lord MacGuffin left in the mayonnaise.

 * Jossed, but it did bring back Lord MacGuffin

Dark Nella is the result of Dr. Tease's meddling.

 * After the NChick Lab, Dr. Tease sent Dr. Block into space for some scientifically irresponsible reason. While there, Dr. Block uncovered a quasi-demonic intergalactic force of evil and (either unknowingly or unintentionally) sent it back to Dr. Tease. During the X-Men review Dr. Tease thought of cloning Nella. While Lindsay was changing her shirt, Dr. Tease dug up Nella's body from under the rocks and decided to inject the force of evil into it, which revived her and turned her evil. Possibly Dr.Tease was also going to inject some of it into Mignon before Lindsay stopped her.

Lindsay and Nella will have an I Know You Are in There Somewhere Fight that will force Lindsay to admit how much she really does love her BFF.

 * Win!

Nella's Squee theories...

 * Nella's Squee is the box of My Little Pony figures she used for her pony drama. This was foreshadowed by the picture Lindsay used to "bind" Dark Nella (it was Nella holding one of her ponies). Once Nella sees this, she'll be back to normal.
 * Dark Nella nuked the Trek shirt because she knew it was squee-related.
 * In order to find Nella's squee the Chick will have to find her own squee. She has been told more than once to embrace her inner fangirl.
 * The trailer for the Dark Nella Saga had Nella and the quasi-demonic intergalactic force of evil arguing with eachother, and Nella stated that "She loves musicals". The last review in the saga is for Newsies.

Lord MacGuffin can be brought back to life with any MacGuffin
Well he is the Lord of them, its within reason that he created them all. Either its just due to their connection with him that they bring him back, or he always plants a back-up MacGuffin power in each one he creates.
 * Bit of Fridge Brilliance here, but the exact wording was that he'd injected the mayonnaise with plot device. Not a plot device. Just plot device. The mayonnaise was able to act accordingly because it became the plot device needed at that moment. Explains the teleportation and the resurrection powers that seemingly came out of nowhere.

Nella's Glasses Stop Dark Nella from Returning
In the Jem review, it looked like Dark Nella was surfacing until Lindsey and the Makeover Fairy made her put her glasses back on. There is a piece of Dark Nella from before she cloned Nella still within her. They learned about this and her glasses is either technology or magical to suppress the evil within their friend.
 * This one is partially true. But I think it operates more on the fact that Nella had on make-up. So the glasses sort of counter-acted it making her Hollywood Homely. It seemed the whole thing operated on Beauty Is Bad.

Dr. Block's husband died in Rio
That's why you shouldn't ask her about Rio: she knows that there's something missing from her memories there (thanks to the chip implanted by Tease), and thinking about it too much causes her severe mental stress. Dr. Tease, of course, finds this incredibly amusing.

The Lupa<-Todd<-Chick<-Linkara love conga will extend to the entire site (or as much of it as possible when taking into consideration sexualities and the amount of women.
It will then become the plot of the 5th year anniversary, which will be a romantic comedy.
 * And Lupa will have a crush on Phelous and as a cute Actor Allusion, he does for her as well.