after completing the game on normal, I started a new one on hard. by the time I went to face Braccus Rex, my party of four is at level 9. and...Rex and his mob are around 9 as well. this battle still took me several tries, since few times I couldn't survive Rex 's initial meteor shower. the whole boss fight is actually quite manageable except for that one spell.
I don't have problem with bosses having various immunity or abilities, but they shouldn't be able to cast spells beyond their levels. facing a level 18+ boss I'd be fine with dealing with meteor shower, not a level 9 one~
