I don't suppose its possible to make an easy custom battle system in RM2k/3 is it?
You're kidding, right? 2k3 is all events. Scripting is much, much smoother and easier to work with, but some things are just really difficult. But eventing an entire battle system? You'll have to find someone really generous, or learn to make one yourself. They're more used in XP because you can add a script that complements the script, and some things scripts can't do.
BUT you could probably put some scripts together, along with events. Like getting one animated battler system, another turn based system, and placing an event where when you meet it it activates the battle screen. I've never played Paper Mario before, so I dunno if this is what you're looking for.