Guide:Emulating link features
(Written by: Kimbles)
This page will explain how to emulate the link features in the Medarot games over the internet or between games on your own computer.
GB/GBC games: Use BGB
For these games, the easiest method for trading and battling is to use BGB (a GB/GBC emulator). It can do internet, LAN, and same-computer connections.
Linking on the same computer
To trade with yourself on the same computer, start by opening two instances of BGB and load up the ROMs that you want. Note that if you want to use two different saves for the same ROM, you'll need to rename one of the ROM/.sav file combinations or put it in another folder for the emulator to treat them seperately (unlike VBAlink, where you number the save files).
(For those not familiar with BGB, you access the menu by right-clicking the screen area. It accepts regular .sav saves, but save states from other emulators are incompatable with it.)
Once both ROMs are running, on one of the BGBs, open the menu -> Link -> Listen, and use the port it gives you (it shouldn't matter since you're on the same computer). On the other BGB, go to Link -> Connect and enter 127.0.0.1 (which should be the default). If it works, both windows should say (linked) in the title bar. Now you should be able to talk to Milky and access the link menu in both instances of the game.
One slightly annoying thing about BGB is that you can't have keyboard input work for both windows at the same time (though there's an option to allow it for gamepads). If you're using a keyboard, you'll need to switch back and forth between the windows to control them.
Linking over the internet
(Note - untested!)
In theory, this is the same as connecting to yourself, except the person connecting needs to actually enter the IP/port they want to connect to.
If you're the "listening" player, open the menu -> Link -> Listen and enter the port you want to be connected through (which ideally should be forwarded). If you're the "connecting" player, go to Link -> Connect and enter the IP of the person you're connecting to, followed by a colon and then the port they selected (IP:port). If it works, the window should say (linked) in the title bar, and you can both talk to Milky and access the link menu.
What about VBA Link?
VBA Link apparently works for GBA games and some GB/GBC games, but not Medarot 1 (I tested it). I haven't tried it with the other games yet.
Other options
There's another GBC emulator called TGB Dual which was specially made for link cable features. The program was originally in Japanese but there are English translated versions floating around.
I haven't tested it over the internet (apparently you need Hamachi), but I played a few M1 battles on the same computer. Bizarrely, the two screens couldn't seem to agree on how the battle was going down, even though the result ended up the same. It's entirely possible it was caused by issues with its link cable emulation, considering it's a fairly old emulator, and I didn't have the problem when I switched to BGB.
GBA games: Use VBA Link
(to be added)
Medarot R: Any working PS1 emulator
This game takes an interesting approach (being a console game) and simply lets you battle and trade between save files on different memory cards. The easiest way to trade with yourself is to copy your Medarot R save onto the second memory card (or just copy the memory card 1 file and rename it so that it's treated as the memory card 2 file).
The official guide book even recommends creating multiple save files and trading with yourself to get more parts from Medarots that you only get to battle a couple of times (like Kantaros). So don't worry, it's officially-sanctioned cheating!