I thought my last post deserved some more explanation.
I'm fairly certain that the elements and status effects in FF1 are a lot more orthogonal than FF Hackster illustrates. Here is what I've been able to determine:
Elements:
1: Stun
2: Poison
4: Dimensional
8: Death
16: Fire
32: Ice
64: Lightning
128: Earth
Status:
1: Death
2: Stone
4: Poison
8: Darkness
16: Stun
32: Sleep
64: Mute
128: Confuse
These seem to be consistent across spells, enemy attacks, weapons, armor resistances, etc. In FF1, you don't get immunity from status effects, you get resistance from elements. So if you resist the "death" element, RUB and XXXX don't work on you, but BANE and QAKE do. If you resist poison, you're safe from BANE, if you resist earth, you're safe from QAKE. A particular source of confusion is the ARUB spell, which I believe grants you resistance to the stun, death, and earth elements (again, not status effects).
We have EVEN MORE themes now, but some old ones are gone...