In honor of the forums returning, I wanted to share a few interesting battle mechanics I noticed in S4 when testing the game a few years ago. My apologies if any of these were shared before:
1. The maximum damage from magic spells is capped at 50% above the base damage. While adding more MAG above this point will not result in more damage, it will allow the damage to ignore magic defense more.
2. Enemies appear to have some fixed minimum/maximum damages. This appears to be bugged in some manner as if you add more defense after you hit an enemy's minimum damage, this can actually increase the damage they do.
3. There are a variety of things that appear to effect speed (it's been a while and I did not take notes on these, so this isn't fully fleshed out. I know there are a few weird speed scenarios I'm forgetting).
a. IIRC, being attacked can completely mess with speed. If you haven't already acted in a turn and you are attacked, your turn goes off at a somewhat random speed. If the final boss goes first and uses an MT spell, the speed at which your PCs go in the same round gets completely scrambled.
b. Casting multi target spells appears to lower speed by around 10 points
4. I believe that weapons might have some effect on crit/evade (for example, I believe bow and dart users evade far less often). They certainly have an effect on countering since at least a few weapon classes can not counter.