I should release that game i started making with RPG maker 2000. Bound to make some money. Although i was like 13 at the time.
Random battles happen because of "balls" that bounce around the screen and when they hit your character you're in battle. The balls are invisible. That's the only way i could figure how to put in "random chance battles".
The battles themselves were "secret of mana" style, where your sword hitting them, does damage, and they die when they have no hit points.
Graphics looked like this:
Except drawn by a 13yo who drew like a 3yo.