Action Replay or Gameshark 3in1/4in1 or memcard (Cheap on Amazon $29.99 http://amzn.to/2icTSGk)
Atlus installer disc burned to CD-R
Sega Saturn Console (Any region)
A real Saturn game of your country code (Jap/US/UK)
Backup game burnt to a CD-R to test (Make your own or find on google)
You will lose the save backup and cheat codes function of your Action Replay, Memcard or Gameshark.
This basically turns those carts into a portable modchip.
You will need to perform the swap trick once to boot the installer disc.
Atlus installer https://firedrop.com/ffe35ab2fc8dc1a4
Unscrew the Sega Saturn console
Take lid off
Tape the lid switch located at the back left together so the Saturn thinks it's closed whilst the lid is off. Swap trick to boot Atlus install disc (Details below on how to do the swap trick) Pop the Action Replay/Cart into the Saturn and press Start
Press Start again
Scroll all the way down to FIRMWARE and press A
Scroll all the way down to another screen to PS031.bin and press Start
Scroll down to Flash Action Replay and press A
Press A again
When screen changes to Action Replay Flasher screen, press and hold A+B+C and then press Start
Wait until it clearly says DONE (Takes about a minute or two)
Turn off Saturn, remove tape on lid switch and screw Saturn back together
Boot Saturn with Backup in the drive and the Cart in the slot
Choose Start Game and you are done.
How to swap trick
Start Saturn with Atlus installer in the drive (No Carts in Saturn)
When you hear the first sound of the drive laser moving "bzzzt" swap for a real game
When you hear that sound again "bzzt" swap for the Atlus installer again
It should now load the Altlus installer.