I decided I would poke around with the GBA Phantasy Star collection as I've only played the first so far and have been wanting to get to II for the longest time. I didn't want to grind so much, though, so I figured I would make myself an easy-mode patch like I made for the first - find the monster data, edit the XP and cash reward values. I've managed to find the monster data in the ROM for PSII, but only for the Fire Ant. I don't know how to read/understand the data for the other monsters in the bestiary.
For reference, I found the Fire Ant's data around address 0x3d7bd0. (It gives 3 XP and 5 meseta, that's what I used as a guide) In RAM, whenever a monster gets loaded, their data gets stored around address 0x02003d70. I'm using the USA version of the ROM. Also, I can't see the monster names in the ROM at the moment, I don't know how they're encoded in there.
If somebody more knowledgeable about GBA hacking and/or Phantasy Star II would like to leave a few tips, it'd be a wonderful help!