Searched google a few times and can't really find what I'm trying to look for. Is there a script which allows to have random bonuses sometimes popping up each turn like "HP MAX BONUS" or "DEFENSE BOOST BONUS" sort of thing. Ask if you want me to be more specific for you, thanks XP.
Actually, I think an easier trick might be a Combat Event triggering at the start of each turn, with a randomizer.
Don't think you directly need a script, but you can use battle events for exactly that. Edit: Warpmind beat me to it.
Well, simplest way might be something like this (copied to each Troop; less laborous than it might seem, since there's no further refinement necessary for each iteration): https://drive.google.com/file/d/0B7syyAkJltVAMUlpNHM0bjVrTlk/view?usp=sharing (I'm having difficulties with posting images. )
First line sets the Battlebuff variable to a number from 1 to 10; the three next items check whether the variable is either 1, 5 or 7, and applies a State if one of those three, well, applies. If 1, add the HP Regen state to the party, if 5, add the Confusion state to all the enemies, if 7, add the Counterattack state to the party.