Guild Wars 2

I was noticing that I never see poison stacked. If there is a poison on a mob and I apply mine that stack size doesn’t go up.

Am I still damaging the mob with mine, as well as the other persons poison? Or does it only reset the timer?

Poison and a few other conditions (burning, for example) don’t stack with intensity, but duration.

You can see which conditions stack with duration and which stack intensity by looking at the wiki page for conditions: http://wiki.guildwars2.com/wiki/Condition (there’s a list of conditions a short way down the page).