I find this very amusing while testing my hack for spell learning...
Well, we know that Poison/Venom the black magic spell sucks huge balls... but it always works even if the enemy is Undead or has Poison resistance (the boss bit is the only saving grace).
If we increase the damage of the spell AND make it multitarget all enemies only (like the Poison attack Dr. Lugae uses), some of the known rules do not apply.
For instance, the spell would work on monsters with the boss bit.. even if you configured the spell to NOT work on bosses!
Additionally when used on any monster that has Darkness elemental resistance, the Spell Multiplier is set to 1 for that target (the monster will not Absorb the damage even if that property is set).
The most amusing part is it also works against magically immune targets! (These are monsters with magic defense set to 255 initially.)
Clearly sloppy coding... but go figure!

Undead are not affected... it is Darkness elemental resistant monsters that are affected.

Edited title for spelling fail