Fandom's a funny thing, isn't it? When a new SegaWorld opened up on the slightly tatty seafront at the foot of Brighton's Madeira Drive a good few years back, I was at the peak of my obsession with the company who'd brought blue sky joy to so many. And so I decided to head down to the opening in the Sega T-shirt I'd made myself to show my support, and at least one person appreciated the effort; someone in a slightly tatty Sonic the Hedgehog costume, who gave me a big, bright blue lollipop that had been reserved for winners of the colouring-in competition they were running that day. I was 21. I still have that lollipop, and I'm still proud of what I did.

Some acts of fandom are a little more productive, though. Like those of Christian Whitehead and his cohorts, the Melbourne-based developer who's been behind a string of spectacular Sonic remakes, all climaxing in last year's outstanding Sonic Mania - a slice of pure concentrate fan service, ushered into life gracefully by Sega and offering an undoubtable high point for the series in some years. Not bad work from a small gaggle of enthusiastic Sonic fans given the keys to their favourite franchise - as well as a guiding hand from the people behind it all in the first place.

"The first game I ever really played was Sonic 2 - and that really set off my interest in video games," says Christian Whitehead over a slightly fuzzy Skype connection. "There was this special cheat debug mode, and for me it was the first time you could see some of the tricks of how games work. That really sparked my curiosity in how games are developed."

"I really loved those 2D games. At least in Australia, the experience with Sonic after the Mega Drive era, the gaming world was very much focussed on PlayStation and Nintendo 64 - I had an interest in those systems, but at the same time I wanted to play *more* 2D Sonic. I could never be satisfied with the first four games. Once I started tinkering around and making the games - I was a teenager then - I wondered if I could make my own Sonic. I used to draw pictures of new levels as a kid.

"It was just a naive sense of let's try it and see what happens. In terms of doing games professionally or even working on Sonic, that wasn't a thought in my mind. My perception was that Sega and Nintendo were companies on the other side of the world, we just saw the games that came into Australia. It was before the internet really transformed the landscape for how people collaborate. My view was that there aren't any 2D Sonic games any more. So I'll have a go fiddling around myself as a 14-year-old kid."

That fiddling eventually led to the creation of several fan games, perhaps the most famous of which was 2008's Retro Sonic - an exacting, excellent take on 2D Sonic that ran on the Dreamcast and was powered in part by Whitehead's own Retro Engine. The perfect tool, it turned out, to get some of the older Sonic games running in the nascent world of mobile gaming where Sega had started to dip its toes, releasing iOS takes on the likes of Super Monkey Ball and an emulated version of the original Sonic the Hedgehog. And so Whitehead set about creating a proof of concept, getting Sonic CD - one of the more ambitious games in the series - up and running on early iPhones.

"At that time mobile phones didn't have the power to emulate Mega CD," explains Whitehead. "But my engine was like a rebuild of the game, and it could run at high speeds. I saw a potential to get an in to do that - and get an in into mobile development in general. It's a specific skill-set I have with Sonic, and I thought it'd be a good way to leverage that and get into professional development."

It took some convincing, but in 2011 Whitehead's version of Sonic CD came out on mobile as well as seeing a release on Xbox 360, PS3 and PC. Sonic CD came at a time when Sega was rediscovering classic Sonic, revisiting classic levels in Sonic Team's Sonic Generations and returning to 2D Sonic gameplay with Dimps' Sonic the Hedgehog 4. They were noble efforts, though something felt off with how they played.

"The modus operandi there, I feel, was that they wanted to present those original levels in the highest fidelity possible at the time with Sonic Team's engine technology," says Whitehead of Generations, who's understandably too polite to be critical of those other games. "It looked stunning, visually, it was all up to 2011 standards."

There's a secret sauce to Sonic, though, that those games had been lacking. And that Whitehead seems to know intimately having dedicated so long to reverse engineering those classic games. So what exactly is it?

"It's interesting with Sonic," he says. "There's a lot of different fans, and they all have different feelings on what Sonic is to them. So I can only use what my own personal feelings are for Sonic, and for me it's always been... Obviously the character itself has very appealing design, it's very iconic. For gameplay there are a lot of inspirations from pinball - all these outside elements - almost skateboarding, really, the idea of picking up speed as you roll down slopes. It's all these physics interactions.

"The core premise of the game is really simple - it's just get to the end of the level and win - but there are so many different ways you can interact with the stages, picking up speed at certain angles, jumping off at certain angles. It's got a very playground feel. Going fast feels good - and at the time on the Mega Drive that was a very impressive technical feat - but also the freedom of gameplay, it's what appeals to me as a Sonic fan."

Whitehead gets what makes Sonic tick, which is no doubt why Sega entrusted him with Sonic Mania, developed in partnership with the company and with input from a number of other dedicated Sonic fans. All these people, we all met in Sonic communities," says Whitehead. "Once the internet got going people would put up stuff and a lot of people have similar feelings and interests. And it was amazing seeing all these people with different talents - music, art, level design - and it just snowballed from there."

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It was a remarkably international effort on Sonic Mania, the developers and producers split across Melbourne, Portland, London and LA - plus, of course, Sonic Team providing its own input from Tokyo, all of which amounted to something approaching a 24-hour development cycle on the game across the clash of timezones. "I have a reputation," says Whitehead. "Even on previous games, I'd earned a nickname as The Vampire. I was on US time. There were some parts of development where I'd get up at 5pm, run a little errand, then work all through the night."

It takes a certain talent to make a really good Sonic game, and a certain skillset that isn't common outside of those that know the original texts inside out. Like those freewheeling levels, racing off in different directions and cartwheeling players around, all while trying to maintain that signature momentum. "I've even spoken to other level designers in the industry and they don't understand how it's done!" says Sonic Mania's level designer Brad Flick. "It's really its own thing - the levels are gargantuan, you're constantly doing a pass and iterating on top of it based on feedback from the internal team, from Sonic Team. To keep that signature flow you could be doing something by moving something in the foreground just ten pixels up."

Sonic Mania's helped by its strong foundations, with many levels built atop older classics - but all delivered with a little twist. "It was good to have a base to work off of, obviously, but we're very ambitious and know these stages have come back before," says Sonic Mania artist Tom Fry. "We wanted them to feel like new experiences in the same environment. Chemical Plant Act 2 really sets that off - it's typically a very horizontal, very speedy stage and then Act 2 is all about moving vertically, and obviously the Puyo boss is a very non-traditional boss. When I was making that, and we were working on the boss, that was wanting to establish the unpredictable nature of the game.

"When we had the brief to include classic levels in Mania, because the precedent had been set my approach was very different," Fry continues. "As a pixelart game we can change the art around, but just doing that alone isn't going to excite the fanbase. My questions were more like, with Chemical Plant - it has this industrial feel, but what else do chemicals do? So in Act 2 I was thinking of the chemistry set you had at high school, and from that idea we fleshed out the vertical gameplay concept with the rebounding gelatinous chemicals."

And it all climaxes in one of Sonic Mania's show-stopping moments - a boss that evolves into a game of Puyo Puyo, a puzzler that Sonic Team has made its own in recent years. "Basically, I came up with the concept for the first mini-boss which was a riff on the original boss in a different way - it's trying to drop chemicals on Sonic," says Whitehead. "Having done that, in Act 2 I was like what on earth can we do? Then I was thinking about chemicals and thinking wouldn't it be funny if we had Puyo Puyo in there.

"When I was presenting this I had no idea what Sonic Team would think about it, so we just put it in the design document and thought let's see what happens. And to our surprise, they were like 'this sounds funny - let's look into it!' Even though it's just a boss, we did a lot of research to properly understand Puyo Puyo. There was a lot of work to make that happen, but it was worth it. When people play that moment, it knocks them for six."

The whole package did, really, and the year since launch hasn't taken the sheen off the team's achievements. Indeed, with this week's release of Sonic Mania Plus, which offers a remixing of the original alongside a handful of new modes, it's a stronger proposition than ever, and through it all the team's enthusiasm for Sonic hasn't dimmed in the slightest.

"I've played those classic levels thousands and thousands of times," says Whitehead, who after all these years is still finding secrets within the original games. "Coming through all that, it's a testament to the games and the original designers that made them. When we finished Sonic Mania I was glad to have a month that didn't involve the hedgehog... I spent a lot of time playing other Saturn games - and I've still got a huge back catalogue of modern titles. The irony is when you're a games developer there's no time to play games. But I'm always happy to go back to those old games. They've got this sense of replayability."

So, what's next for the team - and would Whitehead ever move away from the 2D games that have made his name? "Speaking of games in general I love 3D," he says. "I've worked personally with my own tech with 3D, not for Sonic. 3D interests me as a game developer a lot. It presents a whole different world of design challenges. The retro aesthetic, the reason I started doing it chiefly was that when I was younger - it's a lot easier to develop 2D stuff, because I only had the computer my family had. But to do a 3D game you need a larger team, though personally I'm interested in it. I'm definitely down for it."

Maybe he could turn his attention to some of Sonic Team's other classics. "Well," he says, "we joke about Burning Rangers all the time..."