There's a bit of a problem in that by the second arc, each school (except Balance) has a second school that they boost on. Enemies in the first arc don't boost this way (with the exception of Loremaster), and then by Mirage, these boosts are removed. Btw, here are those schools' boosts:
Fire > Life Ice > Death Storm > Fire Myth > Ice Death > Myth Life > Storm
And then on top of that, there are a few enemies out there with boosts and resists that aren't matched up with other creatures from that school. Hades in Tartarus boosts Balance damage, for example. For the Polaris Key Boss fight, all of the enemies are Shadow. They boost Life and Balance. However, the Sentinel boosts Fire as well. This could be written off as the Sentinel being very Ice-like, but the other enemies do not share a similar boost from other schools. Then, in Mirage, the Scorpion, who is Shadow, does not boost Life or Balance.
Thanks! I didn't know about the second arc, and I forgot what boots balance. Anyways does anyone if there are more? Also I know something always boosts the Astrals so does anyone know? Oh and Shadow, does it have a boost?