If you're lucky enough to still have your original copy or you're looking to experience it via emulation, then you might be interested to learn that there are a bunch of cheat codes for the game which, until now, have been largely unknown in the West.
Randomised Gaming has discovered the codes on a Japanese site and has discovered that they work with the Western version of the game, too – although in some cases, you'll need to create a save file in the Japanese version of the game first.
Here's a rundown of the codes:
Start with Quick Chicken
Enter your name as ZX-9R (use capital letters). Arthur and Melody will start the game with a large number of the item Quick Chicken in their inventory, confirmed working in the PAL version. The Hyphen used is the one next to the / and & signs. Someone at Sonic! Software Planning was a fan of the Kawasaki Ninja ZX-9R motorbike it seems; the downside is you have to put up with a joke name for Arthur for the whole game.
Start with upgrade items, Squeak Sandals & Healing items (Japanese Version)
Enter your name as the following Katakana ダブルオー (Double 00 in English). If entered correctly, Arthur and Melody will start the game with one of each of the permanent stats upgrade items in their inventory Power Juice, Brave Apple, Stamina Onion, Magic Nectar etc.., you will also get extra healing items and a pair of Squeak Sandals. Arthur's name will also revert back to the Katakana for Arthur if entered correctly. Confirmed working in the Japanese version, but the save can be loaded in PAL version.
Access Sound Test & swap Arthur out of the party on any save file (Japanese Version)
Enter your name as the following Katakana シシオドシ (Shishi Odoshi, Deer Scarer in English). If entered correctly, you can now access the Sound Test menu via the option menu screen by pressing the R Trigger button to bring it up. Arthur can now also be swapped out of your main party and placed in your reserve team once you create a savefile with this name. As long as you keep this file, any other savefile the game can see will now gain these features so long as you keep the Shishi Odoshi save. The English version can see a savefile with this name and unlock this feature.
3D Control Pad Support
Insert a SEGA Saturn analogue controller and set it to analogue mode (that's the circle icon on the switch). Then, when in-game, if you press and hold the B down you can look around the screen with the Analogue pad. It acts like a more expanded version of the look functions set to the X & Y buttons.