How does it work? would it be added to spells like bloody pox? would it be added to ill omen? Or only to weapon damage attacks?
If you are referring to the flat poison on it then it only applies to %weapon dmg sources. Same for any other flat dot from gear, devotions, or some skills like elemental awakeningetc.
TY, thought that was how it worked but wanted to be sure.
So, that would also mean if I used 2 attacks with weapon damage, I’d technically get the rat boost on both attacks?
Again just to be sure of how it works 
No, only highest % weapon dmg will really work in the end if it’s a global source like rat and the other examples i mentioned
To explain a little further for Damage Over Time effects ‘weapon damage’ is a single source. So for example, you have a spell that does 40% weapon damage and 100 over 3 seconds poison, and another that does 20% weapon damage and 200 over 3 seconds poison, you’d have the 100 as one source ticking away, the 200 as another ticking away, but only the highest of the weapon damage sources.
Sort of…as best I understand it, whatever poison damage is on the 20% weapon damage still exists, but the highest one will continue to be the one that ticks until it’s duration runs out. So assuming you did the 40% weapon damage attack first it’ll continue to tick until it runs out, and then any remaining duration of the 20% will tick off. Likewise if you recast either of the above (made up) spells before the full duration if one cast crits it’ll be the one dealing damage until it’s duration runs out, but if the 2nd cast has any duration remaining when it runs out it’ll start ticking down. If neither crits they still basically operate the same, but it doesn’t really change anything.
Basically, dots from a single source are tracked, but they don’t stack, if that makes sense. Longest duration will be the duration of the latest application, it doesn’t add the duration to remaining duration of previous, or stack the damage together.
I read a bunch on this recently, and it seemed potentially confusing at first glance to me, so I figured I’d expand on what was said above.
Thanks, that explains it very well