The only real restriction is that I am not counting ports that relied on additional, external support, like the Sega Saturn games that required the RAM Cartridge; I want stuff made with just the core hardware. With that in mind, let's start things off with an example of what happens when a console stays viable for way, WAAAAAAAAY longer than it should have.
Atari released the Video Computer System back in 1977, with the name obviously meant to purposefully trick consumers into buying Atari's console instead of Fairchild's Video Entertainment System (later the Channel F). Eventually, though, the VCS would become known as the Atari 2600, and today it's considered one of the greatest consoles of all time. One of the coolest aspects of the 2600 is that Atari never really meant for it to house complicated games, yet many a designer & programmer found ways to push the system's capabilities, resulting in much more expansive games that what was initially intended. Games like Pitfall II: The Lost Caverns, Raiders of the Lost Ark, & the Swordquest series, among others, were far beyond the scope of what the designers of the 2600 had in mind. Still, those were all original titles... How about when you port over a game like Double Dragon to the Atari 2600?
After a relative drought in the mid-80s, due to the Crash of 1983, Atari decided to bring back the 2600 as a budget-priced alternative during the (rather one-sided) 8-bit battle between Sega's Master System, Atari's 7800 Pro System, & the Nintendo Entertainment System. Likewise, a few developers & publishers supported the returning 2600, one of which was Activision, the first ever third-party developer, founded by ex-Atari employees who wanted due credit for their work. So, on July 23, 1989, Activision released Double Dragon for the Atari 2600... And while I admire the work from Dan Kitchen & his team at NJ-based Imagineering for even somehow making such a port, it's not a good version of Technos Japan's beat-em-up classic. Though it shares the (prior) NES version's two-enemies-on-screen limit, combat is just a chore due to there only being one action button (though most of the moves were kept in!), the playing field is essentially split into two separate halves (made all the more obvious with two players), the enemy AI is insanely tough, & it's just not a fun version of Double Dragon. Activision also released a port for the 7800 at the same time, which is a much more respectable (& understandable) port from another team at Imagineering. Still, what else would you expect from a system that was already a decade old by the time the original arcade version came out? The fact that Kitchen & company found a way to even play this game on the 2600 is a miracle. If you're truly curious, then the cart isn't exactly hard to get a hold of, & if you own an Atari Flashback Portable (which is really one of the best ways to play 2600 games now) then you can grab a rom & play it on there; it works 100% fine.
Though I was a Sega Genesis boy growing up during the 16-bit console war, I won't deny that Capcom tended to show the Super Nintendo more love when it came to Street Fighter. Whereas the Genesis only saw two entries (SFII: Special Champion Edition & Super II), the SNES had double that. While both consoles could handle the CPS-1-powered Street Fighter II (& its Champion Edition & Turbo updates) well enough, the successive CPS-2 was seemingly too much to port over, with only Super II being released on both consoles; a Sega 32X port of Darkstalkers was quietly announced & canceled, though. In 1995, Capcom debuted Street Fighter Alpha (Zero in Japan), a midquel taking place between SFI & II, & in 1996 came its sequel. By this time, due to order from Sega of Japan, the Genesis/Mega Drive was mostly treated like a has-been compared to the Saturn, while Nintendo did the opposite by giving the SNES some respectable attention alongside the Nintendo 64. Because of that, Capcom & Nintendo decided to try their hands at porting over Street Fighter Alpha 2 to the SNES, with it actually coming out in North America first in November of 1996, two months after the PlayStation & Saturn ports came out.
Now, to be fair, the SNES port of Alpha 2 isn't only using the base SNES hardware, but unlike the Saturn's RAM Cartridge, or even the much ballyhooed Super FX chip, the SDD-1 chip isn't quite in the same category as those, so I'll count it. Anyway, the SDD-1 chip (which was only seen here & for Star Ocean) is used for on-the-fly graphics decompression, & it was essential for this port to even be possible on the SNES. Essentially, Capcom compressed all of the necessary sprite data into the game, & the SDD-1 decompresses the necessary character data for each round. Granted, a side effect of this is that each round begins & ends with some minor load times, in order to separately load the needed sound effects into the sound chip, but while this port seems to be more or less maligned by fans, I actually rather enjoy the SNES port of Alpha 2. Yes, the game doesn't run quite as fast as it normally should, the music is simplified, & the voice work is notably compressed, but this is a port that's both a miraculous effort yet also is completely playable & fun on its own merit; it's no replacement for the arcade original, but I think it's given a little too much grief nowadays. Luckily, you don't have to spend the ridiculous amounts that the SNES cart goes for in order to check this out, because it's available on the Wii, Wii U, & even 3DS Virtual Console. Sure, it does technically use extra hardware to be doable, but at least the end result still relies on a stock console to operate.
On the subject of Street Fighter, let's move over to Brazil for the next entry. Over in South America's biggest country, Sega managed to achieve an outright monopoly in that market by teaming with Tectoy to distribute its systems, with the Master System becoming the most iconic of them all. Whereas Sega's 8-bit console was discontinued during the 90s in Japan, North America, & (finally) Europe, in Brazil it never really left; in 2015 it was selling ~150,000/year, rivaling modern consoles like the PlayStation 4 in the region. Therefore, it's not surprising that Tectoy continually put out games as long as it could develop, with the final game being a port of the Game Gear game Mickey's Ultimate Challenge in 1998. One year prior, though, Tectoy would release an original port of Capcom's iconic fighting game, even fooling the gaming giant into approving said game because of what the Brazilians managed to do. In September of 1997, Tectoy released Street Fighter II' for the Master System.
Since there was no version of SFII' for the Game Gear, Tectoy had to make their own version from scratch, and the end result is possibly one of the Brazilian gaming company's finest works. Yes, it only features eight characters (Ryu, Ken, Chun-Li, Guile, & the four bosses), but the Master System port of Street Fighter II' is truly amazing, & an excellent example of how Sega's console was truly the stronger piece of hardware compared to the NES when it came to simple technology. Sure, compared to the arcade original it was definitely lacking (backgrounds are intensely barren, the sound effects are rather weak, & the only voice is of the announcer), but the simple fact is the final product just doesn't look like your "traditional" Master System game; Tectoy even released a six-button controller just for this game. In fact, that ties into the "fooling" I alluded to, since the Tectoy rep hid the Master System from the Capcom rep when getting the proper license approvals for release, & even used a Mega Drive controller to play the game (since it used the same port). After being shown everything, the Capcom rep felt that it was impressive, but not really Mega Drive quality... And then the Tectoy rep revealed that all of this was playing on a Master System. Needless to say, Capcom allowed the use of the license & approved the game for release in Brazil. Today, Street Fighter II' for the Master System is probably one of the toughest ways to play the game legally, since it was only sold in Brazil (& the Master System is region locked), so if you're curious then emulation is the only way to go, but this is truly one of the biggest "miracles" in this list.
Since I brought up Tectoy, then I might as well get to another impossible port that those Brazilians somehow managed to make possible. While not quite the same massive success as the Master System (mainly because it simply couldn't outsell its predecessor), the Mega Drive was still a notable hit for Tectoy, & the company managed to release some games that otherwise didn't see either an official release (Nightmare Circus) or remained Japan-exclusive (Yu Yu Hakusho: Sunset Fighters) elsewhere. In fact, Tectoy's Sega 32X CD release of Surgical Strike remains a bit of a holy grail to this day due to it only being released in Brazil, & with a highly limited print run at that. Still, Tectoy did attempt a single 100% original port on Sega's 16-bit console, & they certainly chose a doozy of a title to get the license to. Seriously, who the hell thought to port Duke Nukem 3D to the Mega Drive & release it only in Brazil on October 12, 1998?!
Admittedly, Duke 3D on the Genesis isn't exactly a 1:1 port of 3D Realms' classic 90s FPS. It only adapted the second episode of the single-player campaign, Lunar Apocalypse, & really plays more like Wolfenstein 3D than Duke 3D. Still, the sprite data for the enemies was there, the (sparse) voice clips from Jon St. John's Duke Nukem sounded respectable for the console they came out of, & it still looked (more or less) like Duke Nukem 3D. In fact, this is one of only four first-person shooters to even be officially released on the console, with the other three being Cyber-Cop, Battle Frenzy, & Zero Tolerance (plus that one stage in Toy Story), & all utilized different ways of simulating the first-person on Sega's system. Tectoy's inspiration actually came from Phantasy Star on the Master System, with the end result being the use of a dithering technique to allow for more on-screen color. Really, the only major flaw with Duke 3D on Genesis is that it's difficult to the point of feeling unfair (& the music isn't the greatest, either). Still, the game remained a bit of a legend in the franchise's history, & on October 16, 2015, seventeen years later, Piko Interactive gave this specific port it's first-ever worldwide release, officially licensed from 3D Realms (shortly before Gearbox Software would win the rights following a bitter legal battle) & everything. In fact, Piko's release is ever-so-slightly better, like including an on-screen crosshair so that you know where you're shooting, that lack of which only added to the Brazilian original's difficulty. Honestly, it's just awesome that something as oddball & bizarre as this has been given a second chance, & I think it's a must-have for any Genesis/Mega Drive collector, if only for the bizarreness.
In the second half of the 90s, the video game industry moved on to the digital medium known as compact disc, allowing for larger games & so much space (for the time) that some studios just didn't know how to fill all of it up, which admittedly helped to the rise of the FMV genre. Nintendo, on the other hand, doubled down on cartridges, and that obviously meant that the Nintendo 64 missed out on a ton of iconic games due to the fact that, at best, a cartridge could only hold barely 10% of the space that a CD could. This became even more obvious when companies started releasing games that took up more than one CD, which was simply not something viable for cartridges from a simple cost perspective (it wasn't "impossible", mind you, but actual examples are scarce). Still, Capcom has already been proven as being up for supporting porting challenges in this list, & easily the most insane of them all was when they decided to release Resident Evil 2 on the Nintendo 64 on October 31, 1999 in North America (Halloween, natch); European & Japanese releases would happen in 2000.
Truly, RE2 on the N64 is the most impressive & mindbogglingly miraculous impossible port on this list, and it's easy to see why. This was a game that featured pre-rendered backgrounds, full motion video cutscenes, lots of voice work, detailed 3D models, & two campaigns that featured their own exclusive content. In fact, Capcom originally released the game across two CDs, one for Leon Kennedy & one for Claire Redfield, but while most people state that this port housed "two CDs worth of content", that's not really the case. The double CD release was mainly for easy separation of the campaigns, but in reality the two shared most of the same assets, so it wasn't like this port somehow crammed 1.4 GBs of data into a cartridge, because it obviously didn't; hell, even the digital release on PSN is only 757 MB, barely larger than a single CD. Still, the team at Capcom Studio 3, Angel Studios (now Rockstar San Diego), & Factor 5 (for sound compression) somehow managed to put almost all of RE2 onto a 64 MB cartridge, with (to my knowledge) only a single cutscene from Claire's campaign being excised & replaced with a similar one from Leon's. Not just that, but the N64 port even has exclusive content that has yet to be included in any other version of the game, like the Ex Files that explain both past & (then) future plot for newcomers, a randomizer for general use items like ammo & health, alternate costumes, blood & gore options, & even an option to change the controls from the traditional "tank" style. Factor 5 even reworked the music at a higher sample rate, making it sound better than on the PS1 (& in Dolby Surround, too!), though voice work & sound effects aren't as crisp. Without a doubt, this is a port that shouldn't exist, but I sure as hell am glad that it does. It's not really a surprise that Angel Studios would go on to create Red Dead Revolver & Redemption, as this game really showed the kind of magic they could deliver.
We're finishing off this B-List with a double dose of Game Boy Color, as both of these games came out in the same year, & I just couldn't choose just one, because both make you question what Nintendo's handheld was truly capable of. First up is Dragon's Lair, the iconic laserdisc arcade game featuring animation headed up by the legendary Don Bluth. It introduced the idea of paying 50¢ for a game, which would become the standard from then on out, showed gamers a brand new visual style of gaming, one that wasn't defined solely by pixels or vectors, & even started the FMV genre in general. Obviously, since it was made using animation that was played off a LD player, porting Dragon's Lair to the home market was initially next to impossible, at least in the way it was at the arcade. Some ports (mainly on the PC) recreated the game to an extent, while others (like on the NES & SNES) simply reinterpreted it into styles that would work on consoles, and when CDs started being used in the 90s accurate ports (or at least as well as the tech would allow) came about. Digital Eclipse, however, seemingly wanted to prove that the arcade game could be done on a cartridge, & decided that the Game Boy Color was the perfect place to show off. After finding a publisher in the form of Capcom (once again proving its penchant for impossible ports), Dragon's Lair for Game Boy Color came out on January 15, 2001 in North America, followed by a European release on August 24.
Later that year, Inforgrames rebooted Frédérick Raynal's seminal horror game with Alone in the Dark: The New Nightmare. Though it was obviously heavily influenced by Resident Evil (bringing everything full circle), it was still a rather cool survival horror game by Darkworks that played up the idea of darkness & shadows excellently by introducing the idea of using a flashlight to light up areas & weaken enemy monsters; the fact that this was done with pre-rendered backgrounds was even more impressive. While Darkworks was getting the original PS1 version ready, though, Pocket Studios was also working on the only other version to come out on the original launch date in Europe, & they also wanted to show off what the GBC could do. Yes, on May 18, 2001, Alone in the Dark: The New Nightmare also came out on the Game Boy Color, complete with pre-rendered backgrounds & a character sprite that seemingly scaled as it moved towards & away from the screen. While HotGen's unreleased GBC port of the original Resident Evil offered a similar concept, it still essentially redrew every background to work with the GBC's color palette. Pocket's AitD, however, seemingly outright recreated the actual backgrounds that Darkworks made for the PS1 original, making it even more of an impressive showcase. A North American release would happen on June 27 that same year, resulting in an interesting case where each territory had a different first impossible GBC port.
Now, to be fair, concessions had to be made for both of these ports to be possible. Dragon's Lair, though recreating a ton of Bluth's exquisite animation into sprite art, didn't include every single room from the arcade original, the sound effects were rather simple (even for the Game Boy), & the music was next to nonexistent. Still, the effort Digital Eclipse put into this port must have been insane, with the end result being impressive, no matter what you think about the original game. The New Nightmare, though looking absolutely amazing, effectively was only half of the game it was on PS1, with Aline Cedrac's campaign missing completely, leaving you to only play as Edward Carnby (word is that Aline's campaign was going to be its own game), items are only indicated on field as a simple yellow icon, & combat was changed completely. Instead of happening in real time, there were sequences (both random & set) were the game would switch to an angled, overhead view & Carnby would have to shoot enemy creatures that come upon him; not the most delicate transition, but it works well enough. Also, if you know what to do, one can beat the game in just over an hour, but that's after a bunch of trial & error. Still, both of these ports truly pushed what could be done on a Game Boy Color, & should be looked at as prime examples that limits are meant to be pushed.
Admittedly, none of these ports are exactly the most ideal ways to play their respective games, minus Resident Evil 2 on N64 (which is generally considered one of the best versions out there), but that was never the point of these ports being made in the first place. For some, it was to let those who didn't "upgrade" be able to experience the same game (more or less) that those who were able to stay "current" were playing. For others, it was seemingly just because a team of developers wanted a challenge & decided to take it upon themselves to make it happen. Either way, these ports are all essential must haves for those who own the systems that they were released on, if only because they can make for good conversation pieces. At least, that's why I have the rom for Double Dragon for the Atari 2600 on my Flashback Portable... Because while it's a terrible port, it's amazing that it was even done in the first place.