I just used VisualBoyAdvance to do this stuff randomly looking for known values and changing stuff. This will be updated as I find more stuff. If you want to hunt for stuff on your own, get VBA, then in tools menu use Memory Viewer. This is how I got a lot of sprites and info. This all mainly applies only to USA Sun Version ROM.
C828 - NOCLIP (kinda)
c828 is the address i found that has something to do with collisions. Put it back to its original value after you walk through the wall you need to! You can enter any hex value between 00 and ff, it will take some experimenting, but eventually you will enter a value which allows you to walk through walls. sometimes, this will result in the map getting scrambled while you are walking. To refresh the area just enter the start menu and come back and things will be normal.
this allows you to skip enormous parts of the game, get to mt. meiji early, leave hometown early, pretty much whatever you can think of really...
Hacking Your Party
for now I have the codes for altering the 1st robopon in your party. these are the memory addresses:
C9B9 - ID
C9BA-C9C0 - NAME
C9C1 - LEVEL
C9C2 - SOFTWARE 1
C9C3 - SOFTWARE 2
C9C4 - SOFTWARE 3
C9C5 - PART
C9C6 - HP
C9C8 - MAX HP
C9CA - EP
C9CC - MAX EP
C9D0 - STATE (scp, nrm, bls, and so on)
C9D1 - ATTACK
C9D3 - DEFENSE
C9D5 - SPEED
C9D7 - exp ( 1 byte ? )
C9DA - TYPE
C9DC - CPU
C9A5 - this address is for the first parts you have on hand, followed by second third at C9A6, C9A7 etc. parts greater than hex 96 are glitched and will crash the game.
CA49 - Hacking Items
for instance, if you put this in, starting at ca49:
36 42 4a 4e
your inventory will be:
mega volt
backupdsk
shortcut
elcmagnet
just be warned: item id ranges beyond 4f are glitch items
CA5D - quantity of items
go to memory address ca5d and you can see the correlated numbers of your inventory. make sure you enter them in hexidecimal:
0a = 10
63 = 99
if you go over 99, youll start getting glitch numbers which is cool B)
C989 - Money
this is the address for money on hand
DF81 - Map Select
When you are on the map screen, you can change this address to select any area of the game to go to even if it isn't unlocked