The original Playstation got quite a few ports of SNK's Neo Geo games, despite the fact that the system wasn't really the greatest home for them- the limited RAM of the PS1 meant that animation frames often had to be cut and load times would be frequent and long (particularly infamous in the port of the first Metal Slug which would stop the action entirely for Now Data Loading!).
However, it seems that SNK and the companies doing the port work did their best to make these ports worth it for the hardcore fans as they often had extra characters not seen in other versions, and in one case having a character otherwise unplayable in the Neo Geo game becoming the protagonist! So, just for a bit of fun, let's take a look at all the examples I could find. Before we start, so I don't have to repeat myself, all of these were Japan-only except for Fatal Fury: Wild Ambition.
Samurai Spirits: Amakusa Kourin Special / Samurai Shodown IV: Amakusa's Revenge Special (1997)
Cham-Cham 
We start with the special Playstation version of the fourth Samurai Shodown game- add this with the stand-alone (and worldwide!) release of III and the Japan-only double-pack of the first two games and you could get pretty much all the 2D Samurai Shodown games on PS1, so that's something! Anyway, the adorable animal girl with a boomerang, Cham-Cham, missing in action since Samurai Shodown II, is available as soon as you boot up the game, but only in Vs. Mode (not even Training Mode!) for player-vs.-player bouts. Her movelist is a little different from how it was in II owing to the changed controls, but it's nice to see her back! She wouldn't return again until Samurai Spirits: Tenkaichi Kenkakuden / Samurai Shodown VI and even later in 2019's Samurai Shodown as DLC. She's a patient cat, huh?
Real Bout Garou Densetsu Special: Dominated Mind (1998)
Alfred & White 
This one's a little confusing so bear with me. This is a very different version of Real Bout Special with the lane-changing removed and a story focusing on new antagonist White and hero Alfred who gets a prominent role in the game's intro. Alfred himself was an unplayable secret boss character in Real Bout 2 which was released a few months before this game, meaning an enhanced port of the previous game in the series got a character you couldn't play as in the most recent installment up to that point. Did you get all that? This game has its own unplayable boss character, as White himself can't be used although unused data suggests that may have been planned at some point. If you want to play as Alfred in Real Bout 2, you'll have to get Fatal Fury Battle Archives Vol. 2 on PS2 I'm afraid! By the way, as pointed out by reader @Kishi in the comments, Airhawk isn't Alfred's second name, it's a fan second name that I'd always seen with the character, but it's not on any of his official profiles, wow!
Bakumatsu Rouman: Gekka no Kenshi / The Last Blade (1999)
Kojiroh Sanada, "Akari" Ichijou & Deku no Shigen 
Oh, three exclusive characters? We're being spoiled in this one! Don't get too excited though, this is mostly a series of recolours and edits of the existing cast, but it might be of interest to big fans of the series. When you first start the game, pressing all four shoulder buttons on the Character Select screen lets you scroll past the list of available characters to select three extra characters- the sub-boss Musashi and two forms of the final boss Kagami. Beat the game once with any character on any difficulty and this area gets three more characters for you to choose- Kojiroh Sanada, "Akari" Ichijou & Deku no Shigen*
Of the three, Kojiroh Sanada is probably the most interesting, as while he's a headswap of Washizuka with minor differences in his super move, he's the brother of Kaori Sanada who impersonates him in the game's sequel which was already out at the time of this port! "Akari" Ichijou (written as AkaRI in at least one guide) is a tanuki impersonating Akari, a swap with a tanuki tail added and graphical alterations to some moves, including a super move involving a tanuki parade. Good. Finally, Deku no Shigen is a fake version of Shigen without the rosary beads and ability to change his skin into metal. These may be mostly palette-swaps, but they do have their own endings if you beat the game with them! You can read more about these characters in this GameFAQs guide for more specifics on the differences.
Garou Densetu: Wild Ambition / Fatal Fury: Wild Ambition (1999)
Duck King & Mr. Karate 
This one's the reason I had to say 'SNK Fighting Games' rather than 'Neo Geo Ports' in the title of this post, as this is a port of the Hyper Neo Geo 64 game, and the only home port of a game from that system (despite the name, Samurai Shodown: Warrior's Rage is not a port, it's a completely different game). It's a pretty neat 3D take on Fatal Fury and the presentation has its charm, although this port doesn't look nearly as nice as the arcade game. Anyway, while Geese and (apparently) Xiangfei were hidden characters in the arcade game, Duck King and Mr. Karate- a version of Ryo Sakazaki from Art of Fighting based roughly on how he appeared in fellow HNG64 game Buriki One- were added to this port, with Mr. Karate unlocked by beating the game without losing a round then beating him (similar to Fatal Fury Special) and Duck King unlocked by beating the game with everyone except Mr. Karate. If you've never tried this one, don't overlook it!
I hope you found this stuff interesting. At some point I need to do the same for the Game Boy Neo Geo ports, almost all of them have extra characters not seen in the original games!
