The unofficial and legally dubious project allows players to traverse Hyrule, the mystical kingdom found in the Zelda series, as Nintendo's portly plumber. The world is a little different to the one found in Link's adventure, however. Hyrule Castle, for instance, is owned by Peach and patrolled by pink Bob-ombs. The Forest Temple, located in the Lost Woods, is filled with colorful Boos instead of flaming skulls. Epona, Link's reliable steed, has been replaced with wooden carriages dragged by overzealous Chain Chomps.

The game is a meticulous recreation of Hyrule inside the Super Mario 64 engine. Kaze Emanuar, a prolific modder, rebuilt every house, dungeon and fairy fountain so it would be recognizable to longtime Zelda fans. Each map was adjusted, however, to accommodate Mario's acrobatic move-set -- unlike Link, the mustachioed hero can wall jump, triple-jump and backflip — and the placement of 170 stars. Some rooms are inaccessible or streamlined so that players can quickly reach the next boss or power-up.

It's a bizarre, but perfectly playable mashup that Emanuar has been building toward for five years. He grew up in the German city of Bremen and discovered emulators — applications that mimic older video game hardware — as a 17-year-old in high school. Most people use emulation to quickly (and often illegally) play titles from their childhood. Emanuar's first exposure, however, was through a Super Mario 64 ROM hack called Star Road. He tried to play it with a mouse and keyboard at first but quickly discovered that a controller was almost mandatory. "Playing Mario 64 mods with keyboards," he explained, is "something you should never do to yourself. If you love yourself, and like anyone, you should definitely go and get a USB controller."

Emanuar enjoyed the difficulty of Star Road, which went beyond the challenges found in Super Mario 64. He had been programming games on his calculator and was instantly intrigued by the N64 modding community. "When I saw that Star Road was a thing, I thought 'Yo, this can be done. If this one guy can make this, then I can make it too.'" His first fan hack was Super Mario 64 Madness, a complete game with custom courses and 122 stars. Emanuar was "a total noob" at modding, however, and the final version was awful. "It's so bad, I hid the trailer from my [YouTube] channel," he explained.

"It's so bad, I hid the trailer from my [YouTube] channel."

Mario fans hated the mod and showered Emanuar with insulting reviews. "They called me disabled and everything," he said. Undeterred, Emanuar released a string of mods in 2013 including the five-level adventure Mario and the Magic Wand, the musical-themed Organ of Matrias, and Super Mario Bros 3D, which lets the player choose between Mario and Luigi. With each ROM hack, Emanuar learned more about the game and the modding tools maintained by the community. These include various open-source level, text and texture editors, as well as custom software for importing 3D object and level files.

Next, Emanuar taught himself assembly (ASM) coding, which uses complex, but still human-readable code and an "assembler" program like CajeASM. The technique is vital for modders who want to differentiate from their peers and add custom features to Super Mario 64. Emanuar used ASM to create Lonely Holidays 64 in August 2013 and Peach's Christmas Invitation that December. Though short, these hacks contained many unique enemies, levels and star challenges. The latter hack, for instance, lets you ride around on Yoshi.

Emanuar hated school. He didn't care much about his grades and planned to study math at University. "For math, you don't need good grades," he said. "So I was just physically there while doing ... whatever." Emanuar would drift off in class and make notes about his next ROM hack. Occasionally he would write assembly code in his folders too. "Just practicing how it works," he explained. "How I could use the logic and the standard better."

The modding took its toll, however. Emanuar was working 17-hour days during the development of Peach's Christmas Invitation. "I didn't do anything but work on that game and sleep," he said. "After that, I just needed a break. I couldn't do it anymore." The modder also felt he'd done everything he could with Mario 64. But he hadn't -- not by a long shot.