With his creative partner Trey Parker, Matt Stone created both the enduringly popular adult cartoon series South Park and the smash-hit musical The Book of Mormon.

Pairing boyish, gross-out comedy with biting parody, they are two of the darkest satirists in US media.

Working with video-game developer Obsidian Entertainment, Stone has spent the last few years both writing and overseeing South Park: The Stick of Truth, a game that's far from the usual throwaway licensed cash-in. Instead it's an interactive extension of the South Park universe, with the same shocking and irresistible sense of humour.

Here he talks about comedy's ever-expanding boundaries and the challenges of writing for interactive rather than passive comedy.

Most licensed video games are farmed out and there is precious little involvement from the people who created the brand. Why did you and Trey involve yourself so closely with the South Park video game?

We did do some cheap licensed games when the show first came out 15 years ago. I think they were on the N64 [Nintendo console] and they stank. We didn't like them. That's why we haven't done one since.

We like video games and it's one of those things that matters to us. Doing a big show there are a lot of licensed products that you have to live with that aren't your favourites, like T-shirts and stuff; that's the deal with the devil.

But when it's a real thing like a video game, it's different. It was the disappointment with the older ones that made us think, OK, if we ever do it again, we have to do it right, or at least intend to do it right, and when the PS3 and Xbox 360 came out we started talking about it.

We could finally do the graphics in a way where it looked like you were in the show.

Why do you think people are more discerning about games now than they used to be?

It was a real learning process doing this, because when you put South Park on TV, it's basically free. You're watching commercials, but you turn it on and there it is. For a video game it's very different. People are spending $60 – or, in the future, when it's in the bargain bin, more like $10 – but for most people it's a big purchase that you might forgo something else to afford.

And even apart from money, it's also a time investment. I don't start a video game until like three people have told me it's amazing, because I don't want to get three hours into a game and have it stink.

I think the way people consume video games and how expensive they are makes it a different contract with the audience. It was the same with Book of Mormon - people are coming to the theatre, they're driving there, they're dressing up sometimes.

It's a lot of money – it has to be on a different level because people consume it differently.

An image from South Park: The Stick of Truth, an interactive extension of the South Park universe.

When South Park first hit TV there was a huge moral panic around the show - 17 years later, how has the American public's conservatism changed? Are there things you could make jokes about then that you can't now?

No, it's all the other way. It's crazily more permissive than when we started. The standards were much, much higher when we started out.

You go back and watch the first season of South Park and it's pretty slow and not the best written and junky-looking, but it would almost play on Nickelodeon at this point.

There are dirty words but, conceptually, we couldn't have covered the material that we do now. And yet, in the first year, that's when we were getting all the calls from the network and we had to fight for it, and that's when we were on the cover of magazines that said: "Don't let your children watch".

It's hilarious, people would probably show it to younger kids now. I think things have loosened up and, generally, I think that's pretty good. It's a lot of the reason why television has become so dominant right now.

Part of it is proliferation of channels and being able to do more shit on American TV. Look where the Breaking Bads of the world go now.

That would not have been a mass-marketed thing back in the 90s.

In Europe and Australia, some scenes in the video game have been censored.

I was told that Australia has different standards. They have their own ratings system, as does Europe, so I was told that we had to submit it for ratings and they come back and tell you this will pass, this won't. Ultimately, the full version of the game is in North America, so at least that version is out there, but anywhere it's censored [in the other version], we just put in little black cards explaining what has happened.

It's not that big a deal. It doesn't change things that much, but we weren't going to change the game downwards somewhere and just not tell anybody. You'll see how ridiculous that is.

How do you feel about that?

It does feel like a double standard, a little bit. We weren't willing to change the content, but also it doesn't ruin the game – it's like 40 seconds' worth of the whole game. As long as we could make a joke out of the fact that they made us cut this, that was fine.

On TV only one episode of South Park has been censored. Would you have had to censor the scenes in the game for TV? Do you think that people feel differently about the same content when it's in a game?

There is an interactiveness that makes it different. In movies and television you can do stuff that's morally grey very easily, because you get to show consequences, you get to show reward, but in a video game there's a reason why everything is a Nazi, zombie, or alien - these are pretty clear moral choices.

There are things that make people more uncomfortable in an interactive world, definitely. But that said, what we had in the game, we could have shown that on TV pretty easily, especially now.

Have the challenges of writing Stick of Truth given you an insight into why games traditionally haven't been very good at comedy?

A lot of comedy is timing and it's hard to control comic timing in an open world where you're not in control of when the joke happens. It's not really a writer's medium, because you can't write and mould and change on the fly like you can in a live show. Timing is one of those things that's pretty crucial to comedy and pretty hard for video games.

Do you think that American comedy has become more permissive during the 17 years that South Park has been on air?

There were always the Richard Pryors and the Monty Pythons and Eddie Murphys.

People have done raw comedy for a long time. That kind of comedy always existed, but it is easier to find on TV and in our living rooms now. But then, so is pornography.

Maybe it's a technology thing as much as anything, but I do think American TV has opened up hugely to a lot that it wouldn't have been tackled a decade ago or two decades ago.

The big great shows that everyone loves now are more adult-orientated – they're more free with language, and it's just great.

The Stick of Truth was released on 7 March for Playstation 3, PC and Xbox 360