Ghosts from the past came back to haunt the doctors at Grey Sloan during this week's Grey's Anatomy.

"Who Lives, Who Dies, Who Tells Your Story," which was written by co-showrunner Krista Vernoff and directed by Debbie Allen (who also recurs as Catherine Avery), marked the show's 300th episode and featured plenty of callouts to those that came before. During the landmark hour, Meredith (Ellen Pompeo), Alex (Justin Chambers) and more were forced to look backward when victims of a roller coaster accident at a county fair sparked old memories.

The episode saw Meredith, Bailey ( Chandra Wilson) and Webber (James Pickens Jr.) treat George (T.R. Knight) and Christina (Sandra Oh) lookalikes, while Alex focused on a pregnant woman who was also a dead ringer for Izzie. For Amelia (Caterina Scorsone), the accident hit close to home when Owen (Kevin McKidd) opts not to perform a cat scan on a patient before taking him into surgery. Knowing that the oversight is what killed her brother Derek (Patrick Dempsey), she makes sure it gets done anyway and saves his life in the process.

TV Guide hit up Vernoff to weigh in on the special episode including that emotional cameo, Meredith's ascension to surgical royalty and what's next for Owen and Amelia, who are navigating through an awkward split.

At the end of the episode, Meredith looks up at the O.R. gallery and sees her mom. Out of everyone she has lost, why does she see Ellis in physical form?

Krista Vernoff: When we were initially conceiving this episode, we had talked about super-imposing all the ghosts of her past into various scenes like [what they] did with Derek in the scrub room after [he'd] already died. But we got to the table read and Shonda said pay Kate Burton to come stand in that gallery. And she was 100% right, that that was the right ghost. That Meredith put to bed any doubt that she was extraordinary and had made her mother proud. [She] completed this journey that started in the pilot of trying to please a mother who is surgical royalty and who has accused [her] of ordinariness. Meredith had a full-circle moment with that particular ghost.

Jackson's speech about her was touching. Was that difficult or easy to write? How many drafts did you go through before settling on the one we see in the episode?

Vernoff: The first version that I wrote, Meredith was accepting that award on her own behalf and there was a camera live feeding into the O.R. We decided after the table read that it was going to be more powerful to ask Meredith Grey to stand there and receive that speech. So the speech that I had written was quite different. The simultaneous joy and discomfort of having to watch a colleague talk about you, and giving that colleague the opportunity to talk about Meredith the way I believe that the fans feel about Meredith felt right. It was easy to write because I've been a fan of the show from the beginning while writing it and I feel all those things about Meredith Grey.

Throughout the episode, Jackson and others try to convince Meredith to get on the plane to go to the ceremony, but they had difficulty getting her to agree. At first it was that she was afraid of flying and then the trauma patients became her priority. Was there another reason that she didn't want to get on the plane?

Vernoff: What I believe is what Alex said is true. She's afraid to fly and she's afraid to lose. And also what Jackson said is true, which is that a trauma came in into the ER and she knew she was the best surgeon for the job. I believe that that juxtaposition, that one can be simultaneously fearful and heroic, is what makes us love Meredith Grey so much. She's not just singularly heroic. She's also driven by fears and insecurities and doubts and she most of the time does the right thing in the face of her fears and insecurities and doubts. That's what makes her a hero that I can relate to and that I think so many people worldwide relate to.

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She's obviously had a difficult journey thus far but more good things seem to be happening for her. Will this upward trend continue?

Vernoff: Meredith has grown up and she has survived a lot of things. And what I believe is that people have to go through journeys of darkness and of light. Those things coexist. Meredith has been through so much darkness that the natural balance is a little bit of light. She has earned some grace. She has survived a tremendous amount of pain, more loss than most of us would deem fair. And people are either destroyed by that kind of loss or they rise from those ashes. I believe that Meredith has risen and we will continue to see her rise.

Bailey is very upset with Ben about pursuing firefighting school, even telling him he has commitment issues. What's she really angry about? Why doesn't she want him to do this?

Vernoff: I don't think there's any one reason. Bailey has a lot of reasons and the mind tells you a lot of different things, but the driving emotion behind that kind of anger is fear and we'll be exploring that more.

This episode featured quite a few easter eggs, like Meredith taking the ferry and the interns hanging out in the tunnel. Were there more planned out that got cut?

Vernoff: No. Every easter egg that I intended made it into the episode and then some. It was really amazing watching the fans and critics make their lists and they hit every one that I had intended and like a dozen more. Almost every word of the script that I wrote made it to screen. Debbie Allen moved [the episode] like a bullet train.

Things are a bit weird between Amelia and Owen right now, especially since she walked in on his naked brunch with Carina. How will they continue to navigate through the awkwardness of this split?

Vernoff: What I love about Owen and Amelia and the way they're navigating this split is that they're doing it with tremendous love and respect for one another and they are being incredibly adult about it. I watched young fans on Twitter going, "Their relationship is just weird!" Because people believe that we have to torture each other, that we have to torture the people that we've loved when we break up...That we have to abuse them and we have to ghost them and we have to be cruel to them online and when we run into them. I'm trying to say no we don't. These people love each other tremendously and they went through something very unique, which was Amelia's brain tumor, and they are both rising so beautifully. It's funny and it's joyful and it's kind and it's open-hearted.

DeLuca is also dealing with his own issues now that his ex has been assigned to work at the hospital. Despite a messy breakup, he still has feelings for her. How are they going to work together?

Vernoff: Sam and Deluca have a really loaded history which we will continue to explore. What I believe about Sam and Deluca is that they were a couple who were genuinely in love but they brought out the worst in each other. And what we've talked about in the [writer's] room is that everyone I know has had some version of that relationship where it's f---ing and fighting and f---ing and fighting and you go, I love this person and this person loves me and we cannot build a life together...the idea that love is only one ingredient in the pie, it's the sugar. But if you don't have the other ingredients that make the pie rise into a pie, you don't have a functional dessert. Sam and DeLuca together do not together make a functional dessert but they also are like magnets and I think it's a lot of fun to explore.

Grey's Anatomy continues Thursdays at 8/7c on ABC.