Metal Slug 1-3 and X (cancelled Game Boy Advance ports; 2005)
Metal Slug is an extremely popular cartoonish run-and-gun series from SNK Playmore that features characters Marco and Eri running and gunning down enemies with various artillery and vehicles. Like any other successful series, it's games have received many ports over the years to many different consoles, such as the PlayStation 2, Xbox, Wii Virtual Console and so on. This is especially true for the very first installment in the series simply called Metal Slug (also commonly referred to as Metal Slug: Super Vehicle-001 and Metal Slug 1 for differentiation).
After the success of Metal Slug Advance on the Game Boy Advance, more Metal Slug releases for the console were given the go-ahead, and the original installment was also set to make a port onto that console. Announced in 2005, this port would remain largely faithful and untampered to its original formula, with the developers claiming they neither added nor removed anything. It would use as many colors on screen as possible for the GBA and was possibly going to be sub-titled "Super Vehicle," which was either just the original version's name or a slightly altered name at that, to separate it as the 10th-anniversary port re-release. It is unknown if multiplayer was going to be included, but it was reported to have a "mission structure." SNK even anticipated more Metal Slug releases for this console, despite the fact that the Nintendo DS and PSP were already on the market. Japanese magazine Famitsu even announced that not only was the original Metal Slug coming to GBA, but also Metal Slug 2, Metal Slug 3 & Metal Slug X. 
It was in a very early state around March/April 2006 as it didn't have anything to properly show at that time, but by May of that year it had background animation and a responsive player, but no enemies. In the same year, IGN revealed another early playable version which seemed port perfect, but it had some slowdown and graphical issues at that point in development that would have to be later fixed. Similarly, at the same time Gamespot said that not all of the actions were fully functional and that it was incomplete, but it was still looking decent, and they were going to see how faithful it would be to the original upon release. It is unknown how far the other three Metal Slug ports had gotten in development (though it's safe to assume that they could have put all of their work into this port first before getting to the rest), but apparently the various gaming websites who got a hands-on with a pre-release version of this port could have possibly played a nearly complete version which was just at the publishing stage.
Planned Publication and Cancellation
Originally planned to be released in December/Winter 2005 and rated T for Teen and distributed by Atari, it would be delayed to September 2006 to mark the tenth anniversary of the original arcade release, and was eventually quietly cancelled, as in October 2006 Famitsu announced that it and the ports for 2,3 & X were scrapped. It could have been assumed that this was because of how long it took to release Advance combined with the releases at a time frame nearing the end of the GBA's lifespan and/or because compilations like Metal Slug Anthology were coming out that would effectively make these releases obsolete, but it was actually quietly announced months later in 2007 on the SNK Playmore USA website that "Due to the limited memory size of the GBA cartridge the plans for MS on GBA has been cancelled." However, it does add "Please purchase MS Anthology on Wii, PS2 or PSP to play the complete game." One person even claimed that he had contacted SNK only to have a representitive say "No matter what, it's coming out. It's a lot of Metal Slug for a small cartridge. It may be limited, but it will come out."
Since then, ports of the Metal Slug games on portable devices like the PSP, iOS, Android and Neo Geo X, as well as inclusions in portable-released compilations like Metal Slug Anthology and SNK Arcade Classics Vol. 1 have followed.
- The Famitsu article referencing SNK's plans for future Metal Slug ports. Last retrieved 22 Mar '17
- A Gamespy article showing off development progress. Last retrieved 22 Mar '17
- An IGN article showcasing a playable version early in development. Last retrieved 22 Mar '17.
- The GameSpot article which reviews another indev version of the game. Last Retrieved 22 Mar '17
- The official announcement of cancellation on SNK's website, after months of fan speculation and articles. Last retrieved 22 Mar '17