Poison damage works much differently in Diablo III than it does in most other RPGs (such as Diablo 2) and Jay Wilson took some Twitter time to try to clarify things.
Poison in D3 does not act like D2. It’s not a guaranteed dot. If a skill has a DoT reapplying refreshes duration unless noted. –JayWilson
with that said, is there a way of increasing the chance to poison the target or is there just a set % to poison? –sebducker
there is no ‘chance to poison’. If you hit, you hit.
so basically the target will only be poisoned by one poison effect,the one which does the most damage for the longest period? –sebducker
So, no DOT. Some skills have DOT mechanics, and some of those skills use poison damage, but poison damage does not DOT by default. –JayWilson
I’ll repeat: poison damage does not work like D2. It does not apply a persistent effect, it’s a type of damage like fire or holy. –JayWilson
I suppose this is simpler, with poison just another type of damage, and not one that works in some special different way than all the others as it did in D2. I can also remember how hard it was to calculating poison damage D2, once you had multiple sources of poison adding DPS, stacking or resetting the duration, etc. That said, it seems weird to rethink it now, since the whole concept of poison is that it takes some time to hurt or kill, whether in real life or video games.
Note that Diablo III has (or had, who knows how things have changed recently) a Disease type of damage which dealt DoT while also adding a reduced damage debuff. (Both Poison and Disease are mitigated by a character’s poison resistance.) Also note that poison damage is often called “Acid,” such as from the WD’s Acid Cloud skill. Confused yet?