If there's one person's head we would never want to get inside of, it's probably Valentine Morgenstern (Alan Van Sprang), but that's exactly what Harry Shum Jr. had to do for this week's episode of Shadowhunters.

Thanks to an unfortunate run-in with a higher demon, Magnus (Harry Shum Jr.) has found himself trapped in Valentine's body, and thus imprisoned in the Institute, while Valentine takes his warlock body for a joy ride. TVGuide.com spoke to Shum Jr. about what it was like to play such a twisted character as well as the old memories that this torturous situation (seriously — torturous) will bring to the surface for Magnus.

How did you even start getting into the headspace to play Valentine playing Magnus?

Harry Shum Jr.: Luckily, we've had a season and a half to really, for me, find out who Valentine really is and what his motivation really is and to see him interact with different characters. I think tapes are the first thing you can kind of look at. After putting that layer on, it's really figuring out what situation he's being put in, in this particular episode.

Outside of getting the mannerisms and kind of becoming him and how he's very manipulative... He is trying to figure out how Magnus actually acts. He's this thing [Valentine] actually hates and despises, but also he has to somewhat find his essence as well trying to throw people off, so he can move on to his next agenda, which is to get out of it.

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To be real though, Magnus got the worse end of that stick, didn't he?

Shum Jr.: For sure. We can talk about Valentine - his worst nightmare is being in a warlock's body, but I think Magnus' worst nightmare is being locked up in a prison and nobody believes - especially the love of his life - believes that he is him. I think it's his worst nightmare. And with that, what they do to him, that puts an extra layer on top of his worst nightmare, which definitely affects him over time.

Outside of the torture and people not believing him and bringing up old, traumatic memories, someone is going to be so fragile after that. Sometimes having a traumatic experience like that, almost no one can help. The only friend that you have is time, and the thing that you can get it giving you time and space or the understanding that this is going to be a long process to get back to his old self. That's the sad part of it all. Magnus isn't even thinking about revenge at that point, he's just trying to get himself level-headed and back into a mental state that's somewhat healthy.

Alan Van Sprang and Harry Shum Jr., <em>Shadowhunters</em>Alan Van Sprang and Harry Shum Jr., Shadowhunters

Will we get to see more of Magnus' past this season?

Shum Jr.: Yeah, I think the writers are really trying to explore that. That is their goal because why wouldn't you? You have this character that is so rich in history, and a lot of his past is something that will affect the future. When you bring that up, he has to navigate it in a different way. For the writers, I think that's really fun as well as for me as an actor. I hope that the audiences really enjoy that ride as well because he is a character that has gone through a lot, and for people to see how he approaches it and how he handles it, I think is going to be a very interesting ride.

Do you think Magnus will pull away from the Institute (and Alec) after going through this ordeal?

Shum Jr.: What I've always known of Magnus is that he's very strong. He's a strong character. I don't think anything or anybody can hold him down. It can stop him for the time being, temporarily.

Obviously he wants to lean on Alec (Matthew Daddario), but also Alec has a lot on his plate outside of trying to help Magnus. He still has to be able to deal with getting Valentine and getting the Mortal Cup and all that, especially dealing with his family as well. So there's a lot for him to deal with outside of just Magnus. Magnus is a big part of his world, but he's not the only thing that kind of keeps him going because he still has his whole other life that he has to pay attention to. It's going to be a difficult situation, and I hope they make it out of it, but they won't be unscathed unfortunately.

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If you could chose two other characters to get the body swap treatment who would they be? Which actors would you want to see do what you and Alan Van Sprang got to do?

Shum Jr.: I honestly think, to play around, the two Parabatais [Jace and Alec] would be hilarious. They, themselves, would be so fun to watch. They've been put in situations where they have to go against each other even though they know that they love each other and they're brothers in that sense... I think them switching bodies would be really interesting to watch. And I'm sure [Dominic Sherwood] and [Matthew Daddario] would pull some pranks along the way as well.

Can you tease anything about Sarah Hyland's guest star role this season?

Shum Jr.: She will be the new Magnus. She will be taking over my duties as Magnus, and I will just be on the sidelines telling her exactly what to do — no I'm just kidding. I can't really tell you what it is, but Sarah is an awesome actress, and it's so good to have her energy on our show. I think people will be impressed with what she's going to bring to the table.

Shadowhunters airs Mondays at 8/7c on Freeform.