It was basically a cartoon version of the formula that Marvel Studios is now mining to great success, and which video games has seen most visibly in Nintendo's Super Smash Bros. games.
We've also had Mario + Rabbids, and the at-one-time-unthinkable pairing of Mario and Sonic in a bunch of official Olympics tie-ins, in addition to the likes of Capcom, Square and Disney, and Konami mashing up various franchises.
Here are ten more of the lesser-known gaming crossovers.
"Hello, Sega Boss-boss. I've invented a new games character who is an ex-husband, and his name is Jeff, and I call him Jeff the Exhusband."
"But please... can't you come up with a better name?"
"Okay. I know. What about Jeff Exhusbandd?"
"I la-la-la-love it!"
Suffice to say, Kidd never scaled the same heights as Mario - or even Sega's own Sonic - and the series probably peaked with his first game, Alex Kidd in Miracle World. Still, they did their best, funnelling out a succession of less-adored sequels, which culminated in what the kids nowadays call a "collab", leveraging the lifting power of another Sega franchise with high visibility.
Alex Kidd in Shinobi World saw Big Ears stranded in Sega's Shinobi series, see. Admittedly, it's more a cutesy parody of the Shinobi games, rather than a bona-fide crossover, but it featured a number thinly-veiled reinterpretations of familiar Shinobi characters.
He received funding following a second pitch, where - somehow - his concept of a surreal business simulation-cum-role-playing game, which placed the player in charge of Sega in the year 2025 when its market share had been reduced to 3% (which turned out to be starkly prescient), was more favourably received. However, at this point in Sega's existence the Dreamcast had flopped, and the company was looking for a console hardware exit strategy.
Segagaga made satirical mention of Sega's Dreamcast troubles, poked fun at the PlayStation, and featured cameos from a host of Sega characters, including the aforementioned Alex Kidd, NiGHTS, Amigo from Samba de Amigo, Ristar, various Golden Axe characters, Ryo from the Shenmue games, and - inevitably - Sonic "the" Hedgehog.
More bizarre still, Karate Kid star Ralph Macchio, for whatever inexplicable reason, appeared in various forms, including as a drill-handed cyborg, and some sort of octopus thing. That's not even me making up a load of random nonsense for once.
When the game shipped, it was buggy, hit with a bunch of copyright claims (from Ferrari to the actor who played Segata Sanshiro, a character from a Sega Saturn ad based upon real-life judo legend Sugata Sanshiro), and had a marketing budget of less than £200. Half of that went on a wrestling mask so that Tez Okano could disguise his true identity while promoting the game.
Again: I didn't make up any of that.
Double Dragon was always about relatively grounded fighting, while the Battletoads are ripped straight from a cartoon, with over-the-top moves and outlandish fisting.
Regardless, being based on the Battletoads engine, the gameplay was far more grounded in that amphibious universe, the end-of-level bosses being a mix of mutant creatures with engorged body parts.
Aside from being a crossover between a video game property and a soft drink, it sort-of-earns its inclusion in this list for resulting in, perhaps, the first intra-platform crossover. You see, Pepsiman later had his own video game on the PlayStation 2. And it was rubbish.
As you can see, Pepsiman is a featureless silver robot, who would appear suddenly to people in crisis situations in order to dispense Pepsi. Sadly, this came in the form of cans or bottles, rather than emitting in from his nip-nips or some manner of built-in "nozzle".
Just ask Bono. He's got enough money never to work again, and could spend the rest of his life helping the impoverished. He doesn't though does he?
No, night after night he dyes his hair and gets up on stage in his built-up heels, and waves his arms around in front of tens of thousands of people going "Oooh, look at me. I'm Bono! LOOK AT ME! You in the front row - why are you on your phone?! You should be looking at meeeee!!! ...Where the streets have no naaa-aaa-aaame!"
Sadly, skating games were probably on the cusp of going out of fashion when Konami released Evolution Skateboarding. This may explain why they chose to conceal a number of incongruous cameos within its ribcage. To wit: Solid Snake, Dracula from Castlevania, and - oddly - Frogger. Other Konami games got the nod in the form of themed levels and music.
The game's engine was later used for a skateboarding level in Metal Gear Solid 2: Substance, thus giving you two opportunities to see Snake perform an "olly blunt".
It's fair to say that the Saturn version of Daytona was compared unfavourably with the PlayStation version of Ridge Racer, and this may well have been the spark which lit the fuse that led to Sega's ultimate implosion as a console hardware manufacturer.
Consequently, there's something about the Hornet appearing in Ridge Racer which I find unspeakably sad. It's like they did it out of pity.
Given the peculiar and surreal sense of humour which runs through them like a worm in a block of cheese, when the apes from Sony's Ape Escape popped up in Metal Gear Solid 3: Snake Eater - in a mini game requiring Snake to catch them - they felt oddly at home.
This wasn't the only guest appearance by the Ape Escape apes; you can also find them in Ratchet & Clank, Monster Rancher 4, and LittleBigPlanet.
That didn't work, of course.
Though NiGHTS Into Dreams has its fans, and was developed by former Sonic Team members, it verged a little too far into the esoteric, and may have been too different to anything else for people to truly grasp hold of. Furthermore, its main character - a sort of purple harlequin dream man thing wearing flares - was never going to be as iconic as a little blue hedgehog in red trainers.
Indeed, NiGHTS, if anything, simply made people more hungry for a new Sonic game. However, Sonic did appear in 3D form in Christmas NiGHTS Into Dreams, a two-level festive giveaway. Once unlocked, Sonic could play through one of the levels on foot (as opposed to the flying which formed the basis of the main game), before confronting a giant inflatable Dr Robotnik.
The cameo did succeed, however, in silencing many of the calls for a 3D Sonic game. When players saw how poorly Sonic controlled in a free-roaming 3D world without a fixed camera, they all pulled a face and went... "Yeah, actually... on second thoughts..."
Following the release of Earthworm Jim 2, series creator Shiny Entertainment was sold to Interplay. The third game in the franchise was Earthworm Jim 3D, created without the input of the original team. It was, with a degree of crushing inevitability, terrible. The character appeared in one more full-outing - the dreadful Game Boy Color platformer Menace 2 The Galaxy - before being put out to pasture.
His only other two appearances to date were as a secret character in the beat 'em ups Battle Arena Toshinden and Clay Fighter 63 1/3. Suffice to say, it was an ignominious end for a character who had been responsible for two brilliant games, and even appeared in his own cartoon series.
However, Jim's creators at Shiny didn't quite let him go, making oblique references to him in MDK and Sacrifice (the latter in the form of a worm god called James).
Electronic Arts' Fight Night Round 2 was - for the most part - a serious and realistic simulation of this so-called "sport". It was a far cry from Nintendo's Punch-Out!! series which, lest we forget, featured dubious "international" competitors such as Don Flamenco, Pizza Pasta, and Vodka Drunkenski (renamed in subsequent instalments to the less contentious Soda Popinski).
The series protagonist, since the very first game, was the nondescript Little Mac. When EA signed a deal to bring its sports games to the GameCube, Nintendo insisted that they also feature exclusive Nintendo content - which is how Little Mac ended up in Fight Night Round 2.
However, whereas Mac had previously been a diminutive, but otherwise average-looking Italian-American, for reasons that are known only to EA, in Fight Night he appeared as a blonde who appeared to have spent too many hours running face-first into a metal post.