Thanks, ZeaLitY! Hopefully I'll have a pretty comprehensive addition to how the 50 odd element modes work.
Some of them are super interesting. Blackhole for instance, uses mode 0x0F, and it's the only element that uses it. On the surface it just looks like an element that does damage and sometimes kills (based on the stat Death, being set), which could also be done with the default mode 0x00. So why add an entirely new element mode? What it actually does is only apply damage if a status effect didn't land. So for instance, if you change the stat block for blackhole to apply poison instead of death, then you'll either damage your enemy or poison them, but not both. My guess is that the developers realized that it would be confusing to show the numerical damage simultaneously to death (it would be ambiguous at least), so they needed this mode to make it clear that non-damage killed the enemy.
There's lots of these little weird and specific modes. More to come soon.