As I begin to completely port my game to ACE, I couldn't find a script like this one. There were random battle BGMs, but sadly I couldn't find any based on actors in the battler party.
This script simply plays a random BGM assigned to actors that are in your battler party.
# No matter how good an RPG's battle music is, players are going to get sick and
# tired of listening to it for the zillionth time. This script won't rid RPG's
# of that problem, but will hopefully stall the process by playing randomized
# music dependent on who the player has in the active party at the start of any
# normal battle.