UPDATE: Already watched the episode? Read what Alex Hirsch told us about the plot twist, celebrity guest and more.

When Gravity Falls left off two weeks ago, it was literally the end of the world as Bill Cipher finally got his wish and crossed over from his otherworldly dimension. Unfortunately for Dipper, Mabel and the rest of the Mystery Crew, that's just the beginning of his dastardly plans for the town—and the rest of the world.

With Weirdmageddon currently underway on the Disney XD animated series, we spoke to show creator Alex Hirsch about what to expect now that the end of the world is finally here. Also, watch an exclusive teaser trailer of Monday's episode down below!

Was it always the plan that Bill would eventually succeed with causing the end of the world?

Yes. There’s a number of things we’ve known from the beginning of the series, from the journals to there [being] an apocalyptic scenario. The concept behind it has to do with finding an external way to visualize what our characters are feeling. In the previous episode, Dipper and Mabel both find themselves confronted with having to take seriously and think about what happens next. What happens after their summer? And broader than that, what happens in their future. Dipper has always been impatient and wants to be taken seriously by everyone and to him the future is an exciting thing he can’t wait to happen. For Mabel, it means a change and potentially an end to the childlike fun and games she’s lived every moment of her life. So when you find yourself at the precipice of a new stage in life, whether it’s a graduation or the end of a relationship or a job, it can feel like the end of the world. And Gravity Falls is all about taking our characters' feelings and exploring them in a big, visual way through the use of magic and mystery. So this idea that those tensions would erupt in an apocalyptic scenario is something that’s been the plan from Day 1.

It was a nice twist to see Dipper more excited and confident about the future and Mabel be the one who’s nervous and insecure for a change.

Mabel feels so confident and happy because she has things the way she likes them. The world that Mabel finds herself in is one where she feels she understands her role in it, and she feels like she knows who she is and where she’s going but without her brother by her side, without her friends, pet pig, or loving uncle. Without that kind of stage for her performance, who is she? That, of course, creates friction with Dipper, which is where we leave off when we enter “Weirdmageddon Part 1.”

What does a “Weirdmageddon” specifically entail? We know what an Armageddon is.

[Laughs] It’s not too mysterious a word. We all understand the myth of the apocalypse as being the horrifying end of all things, where demons reign and law is bended. We definitely follow all those conventions, but because this apocalypse is run by Bill, our most mischievous trickster-prankster-dream-demon, every opportunity for things to be bizarre and abnormal reigns rampant throughout Weirdmageddon. The apocalypse, as you know it, you could expect to see four horsemen. Here, you could expect to see something that is part-horse, part-man and part-spatula speaking French. Things are different, weirder than Gravity Falls normally is.

RELATED: The 6 Things About Gravity Falls That You Need to Know

Does Bill have a specific plan for what he wants to do? Because he’s only ever talked about crossing over and causing chaos.

You will learn more about Bill as the Weirdmageddon arc progresses. He definitely does not believe in rules. And I think that anybody, any kid or adult can relate to the desire for absolute freedom from rules—that libertarian idea of “I do what I want any moment. Damn the consequences.” That’s Bill’s philosophy. It’s a seductive philosophy, [but] as we can see in reality, it can be a literal nightmare. Bill finds worlds like ours that have laws of physics and gravity—and laws at all—to be senseless to him, and it is his irresistible urge to break those rules down. That could sound fun for a while, but our characters discover that there are terrifying consequences.

Dipper and Ford have been fearing this happening for weeks. How will they be dealing with the fact that Weirdmageddon is finally upon them?

This is Ford’s long-simmering nightmare come true. It’s Ford’s fault that Bill was let into our world in the first place. Ford contacted Bill as a way to try to help him with his research, and Bill manipulated Ford into opening a gateway between their worlds. Ford has felt for the last thirty years a profound sense of panicked guilt about being the one to potentially unleash Bill and has made it his Moby Dick-Captain Ahab like mission to take Bill down. So he’s been waiting for this for a long time. In a perverse way he might be a bit excited about it because if it means that he can finally take Bill down once and for all, it will be the grand triumph of his life and his career. But as we’ve seen in his life and in his career, things don’t always go as planned. For Dipper this is an absolute nightmare. Dipper loves the paranormal and the mysterious more than the ordinary life he’s living. Something like Weirdmageddon can almost seem like the dark answer to what Dipper had always wanted, which is a crazy world where magic and mystery were all around, and him and some others were acting as heroes. But when he actually gets it, it’s not as fun as he predicted.

How are the rest of the townspeople coping with Weirdmageddon?

The people of Gravity Falls have a very live and let live attitude. They’re used to odd things occasionally happening and usually they pass them off as an example of altitude sickness. This time around, they are much more terrified and panicked and heading for the hills. Many characters will have roles to play in this Weirdmageddon story moving forward... I can say that we will see Toby Determined in a way that we have never seen him before.

In the last episode, Ford talked about the UFO crash possibly causing the strangeness of Gravity Falls or vice versa. What made you decide that this was the right time to make that reveal?

We’re always looking for a visual, magical metaphor to pair with the character story of the week. This week, our characters’ story was about Dipper and Mabel’s differing attitudes about the future, and that’s a story you can tell without any magic whatsoever. So we knew that this story needed a set piece—a place that kind of was a physical manifestation of the future—of a foreign place that we’re going to. It felt to us that a submerged alien ship had that sort of futuristic technology and a promise for Dipper that his life could be going on adventures all the time if he takes Ford’s answer. So it felt appropriate from a storytelling point of view.

Now that you get to do Gravity Falls' version of the end of the world, were there any movies or TV shows you turned to for inspiration? Or was this something you’d always had in mind?

Our artists and writers on the show have amazing imaginations. Even though it’s fun to work on the show as it normally exists, we always have to maintain ourselves and hold back in terms of weirdness just for the grounded-ness of the episode. So [we finally] had an episode where the doors are open for us and for everybody to go absolutely nuts and write and draw the craziest things [we] thought of. The vision of what this world looks like comes from everyone’s imaginations just unloading into this pocket of an episode. It’s really more inspired by the people we worked with than any particular survival pop culture reference.

Check out the teaser for Monday's episode of Gravity Falls, and then tune in to the episode at 8/7c on Disney XD. For bonus Weirdmageddon scoop, visit TV Insider after the west coast airing.