The HP script you're asking for is pretty specific to that battle script. It's called Rolling HP/PP bars and it's from Earthbound. As a matter of fact that whole battle looks like it came from the Earthbound Battle script which I think can be found on RMRevolution or RPGmaker Revolution.
Anyway, my guess is there's a lot more into it then you'd think but I've always loved the rolling bars myself. Plus it added in the strategy that even if your character dies, if you heal them in time they can still live.