It's no secret that Nintendo has put their most mustachioed asset through an awful lot of work over the decades. Since his very first appearance, the poor sod has been filling in as carpenter, bottling plant worker, plumber, demolitions expert, factory worker, physician, baker, painter, pitcher, archaeologist, golfer, tennis player, soccer player, baseball player, kart racer, mixed martial artist, time traveler, monument, paper doll, graffiti removal specialist, and referee in more sports disciplines than you can count. It's a wonder he still finds time to pursue his true vocation as rescuer of princesses. Guess there's no unions protecting worker rights in the Mushroom Kingdom.

And yet. And yet all that was apparently not enough for the raging workaholic. Maybe he's got a gambling problem, as he has been spotted time and again making more dough on the side doing other companies' biddings. Collected in this dossier are some of his most blatant violations of his work for hire contract he'll surely be one day busted and sacked for, cause as noted no worker protections.

Some rules:

• No mods or romhacks - or else we'd be here all day.
• No homebrew or freeware ports of official games - same reason.
• No officially licensed appearances by other developers/publishers, such as Mario is Missing or Mario + Rabbids.

Candory (1982)

I know I said no romhacks, but I'm going to make an exception right away just for this one because it's super early and was distributed commercially. The game is just a nearly identical clone of the arcade platformer Ponpoko, so much so that the Korean distributor didn't even bother to change the in-game title text. But it does replace the tanuki hero of the original with a certain famous carpenter. (At this time he wasn't even known as a plumber yet!) All the enemies are also changed to various aliens, including other copyright-infringing ones such as E.T. the Extra-Terrestrial.

Firefighter Mario, Mario's Brewery, Pubjumper Mario (1983/unreleased)

At the tender age of 14, Jeremy Thorne programmed not one, not two, but three Mario games. (Firefighter Mario is pictured.) Of those, it seems only Mario's Brewery got published, but the other ones have resurfaced and been preserved since. (Source: Games That Weren't 64)

Out on a Limb (1984)

What if I told you that the first game where Mario had an adventure larger than a handful of screens, as well as the first time he climbed a beanstalk into the clouds, wasn't Super Mario Bros. at all, but an unlicensed appearance in a little known British computer game in the tradition of Jet Set Willy.

Skele Tower (1988)

Skele Tower is a doujin game for Japanese PC-8801 computers that's so obscure I'm not sure you can even find a ROM around. (It's been listed as an erotic title, so beware if you do seek it out.) It's ostensibly a Wizardry-like grid-based dungeon crawler, but without any stats or inventory. Instead, enemies are fought in a 4x4 game of tic-tac-toe. Mario isn't treated well at all in this game - he appears as a mutilated shambling corpse and shouts praise to the "SEGO Mark 3". (Source: PC-8x01 Doujin Gallery)

Alex Kidd in Shinobi World (1990)

In the published version of Alex Kidd's last 8-bit adventure the boss of the first area is just a big dude in a samurai armor named Kabuto, though he does have some peculiar Mario-like traits like throwing fireballs and shrinking when hurt. That makes a lot of sense once you learn that he was originally cast as Mari-Oh, sporting a very characteristic mustache. Early 1990s Sega is no stranger to parodying other companies' IP - see the Spiderman, Batman, and Godzilla enemies in the original version of The Revenge of Shinobi - but maybe after the experience of being forced to change those in the earlier released game, they ended up pulling their punches with Shinobi World. (Source: Unseen 64)

The Adventures of Quik and Silva (1991)

First shipped as a coverdisk for the magazine Amiga Fun, The Adventures of Quik and Silva is an odd little title where all the enemies are corrupted versions of famous video game characters of the time, from Bubble Bobble's Bub to the R-9 starship of R-Type. Perhaps the game is most notable for including Sonic the Hedgehog a month before his first official game was even out, but Mario also got a particularly grotesque appearance - or rather just his disembodied head on a spring. Gnarly! (Source: Larry Bundy Jr)

Super Boy III (1991)

The Super Boy series by Korean publisher Zemina is another edge case for this list. The first two games are just downgraded ports of Super Mario Bros. for the MSX, whereas the fourth and final entry replaces Mario with an original sprite while still stealing many graphics from Super Mario World. Only Super Boy III features Mario himself in an unique yet familiar adventure, culling elements from both Super Mario Bros. 3 and Super Mario World, some hilariously adjusted for the MSX's limited graphics capabilities, like the wobbly diagonal pipes.

Dooley Bravo Land (1992)

During his second tenure working undercover in Korea for the Super Boy series, Mario also found some time for a smaller role in this unreasonably tough platformer based on an popular old cartoon for kids. Didn't even bother to get a disguise and just appears in his Super Mario Bros. 3 outfit.

Battle Mania Daiginjō (1993/12/24)

Battle Mania may feature a zany setting mixing Japanese traditional imagery with cyberpunk, horror, and a whole lot of cartoonish characters, but there's also some space for our dear serial part-timer in this side-scrolling shoot-em-up. Even if it's just a blink-and-you-miss-it flyover attack, there's multiple clones of him passing by at once. He appears a bit more muscular than usual, but his costume is unmistakable, even including the cape from Super Mario World. (Source: Hardcore Gaming 101)

Astal (1995/04/28)

Another job opportunity that didn't quite pan out. When you play this gorgeous-looking 2D platformer, Mario is nowhere to be found. But by poking around the files his image can be restored in a rather suspicious-looking pose. It's unknown what it was meant to be for, if anything at all. (Source: The Cutting Room Floor)

Daraku no Kuni no Angie: Kyōkai no Mesu Dorei-tachi (1996/04/19)

This time Mario's brother Luigi tags along, and the two turn uncharacteristically naughty. The two bros. worked out quite a bit for this role and use the code names Marao and Igilu, but they're not fooling anyone in their spandex suits. While loosely inspired by Alice's Adventures in Wonderland, Daraku no Kuni no Angie is a porn game through and through, so keep that in mind if you seek out further info on it.

Asterix & Obelix XXL 2: Mission: Las Vegum (2006/06/30)

The second Asterix & Obelix XXL game takes a much more self-aware and fourth wall breaking tone than the venerable French franchise usually does, and many of the Roman enemies you get to slap resemble characters from other video games. Mario appears complete with his cleaning gear from his then most recent main game, Super Mario Sunshine, which he uses to hose down the two Gallic heroes.

The Binding of Isaac (2011/09/28)

The stunningly deep action-roguelike The Binding of Isaac features a plethora of hidden items and characters. Among the co-op mode exclusives, more than just a few directly reference the Mario IP. The hero himself is only referred to as "Red Plumber Baby". (Source: TheGamer)

Zombie Run (2012/06/19)

The Zombie Run games are pretty standard Temple Run clones with the twist that you play as the hunter instead of the hunted, which in an endless runner has surprisingly little bearing on the gameplay. Its one true hook is the many playable characters that are unlicensed zombified versions of popular characters. In Zombie Run 2 (the only one still playable on my old smartphone), the massive Zombario is one of the last unlockables on the extraordinarily grindy upgrade tree.

Hitman (2016/03/11)

In the Hitman reboot's Sapienza level, you get to encounter the "Saltatore" brothers Mario and Luigi, wearing a more grounded version of their iconic colors. This being a Hitman game, it's no surprise that there's also a sadistic optional contract where you're tasked to murder them both wearing the other brother's outfit. (Source: outsidexbox)