When Riley and Maya first meet Farkle, he is dressed as Dracula. That's no accident.
Dracula and Farkle have some things in common.
For one, they don't have a lot of faith. And two, they fall for the innocent and loving princess in their story.
In the original novel Bram Stoker's Dracula, the vampire was more than just a blood sucking fiend. He was a count, and he desired power and control. When he lost it all, he cursed God, renouncing his faith in him, and he became an undead (neither dead or alive) and fed off the blood of others. His true love dies, and he believes that Mina is her reincarnation, because she is kind and loving.
Mina is the wife of John Harker, who doubts himself. She wants to be like her friend Lucy, and she is often related to mentions of light throughout the narrative.
Before Dracula pursues Mina, he seduces and transforms her friend Lucy into one of his followers.
But, his pursuit of Mina is very different. He courts her, playing the role of a lover, but when Mina discovers who Dracula is, he is ashamed, and he refuses to transform Mina into a mindless follower.
He wants to make her his equal, and he promises her eternal love. Mina agrees, but Van Helsing interrupts the ritual.
When Mina is under the care of Van Helsing and Harker, she feels connected to Dracula, and she wants to save him. Darkness desires light and light desires darkness.
At the end of the story, Mina makes a choice. She kills Dracula, after Dracula himself begs her to do so. He no longer wants to be between life and death. After driving a stake through Dracula's heart, Mina tells him that she loves him saving everyone from darkness. In the end, Mina returns to Harker, and they live the rest of their lives together.
So how does this relate to Farkle? Well, Farkle has a lot of doubt in things that cannot be proven. He's cynical about things that can't be explained by science, and he likes to be in control. (He is like Harker in this way)
We see this dynamic from the beginning in the Pilot when he claims that Riley is the sun and Maya is the night. He has already set up the rules for Farkle Nation, which we see the outcome of in both Girl Meets Friendship and Girl Meets Crazy Hat. He wants to rule the world. He desires power.
But, he also holds Riley in the role of the angel, and often treats her differently than Maya. Around Riley, Farkle is supportive, caring and attentive. Around Maya, he is a major flirt with hardly any substance.
In Girl Meets Farkle's Choice, Farkle tells Riley, "there is only you." But, he still flirts with Maya, and he eventually steps back.
He doesn't feel like he's part of the story. His role is in limbo, between the ideal of Lucas and the rules that Farkle himself created. (Neither living nor dead)
In Girl Meets Flaws, we learn that Farkle is ashamed of who he is. This is a reoccurring theme in the episodes Yearbook, I Am Farkle and Girl Meets The Great Lady of New York.
Riley and Farkle have an emotional connection. They know when something is wrong with each other. Only Riley can reach Farkle emotionally. And, she has "saved" him a few times in Flaws, Yearbook, I Am Farkle, Money, and Great Lady of New York.
But despite Riley's obvious attention to Farkle, Farkle pushes Riley towards Lucas in New Years. He doesn't believe that Riley loves him, even though both said so in Texas 3.
So, the allusion of Dracula relates to Farkle and Riley's narratives.
Dracula represents the dictator side of Farkle, the logical side that wants to be in control. As Farkle denies emotion, he gains more and more power over the characters that he has influenced.
Harker represents the human side of Farkle, the real Farkle. The sweet, observant and loving guy that has been a part of Riley's life this whole time. Even though he doubts himself.
Mina, of course represents Riley, who is often the "light" in Farkle's life, who can reach him emotionally.
Farkle wears turtlenecks because he's afraid of vampires. Why?
A vampire archetype is a manipulative person. Farkle fears the realm of emotion, and the unknown and illogical world of feelings. He doesn't realize that he has become what he feared. (like Batman)
Farkle is manipulative. His concept that Riley is the sun and Maya is the night has controlled the Purple Cat World from the beginning. Farkle forced his logic on the two girls to avoid having feelings for them, but those feelings were already there.
It's obvious. He loves Riley, and he has since the moment he "saved her life". But he refuses to acknowledge that. So, he forces his logic on others (like he did on Riley in New Years). As a result, he walks in limbo, neither part of the story nor not part of the story. Until Farkle realizes what he has done, he won't acknowledge his emotions. And because Riley can reach Farkle emotionally, she needs to save Farkle, from himself. From the idea that Farkle has created (that he is nothing). Only Riley can help Farkle understand love.