How Does The Plague Staff Work?

Recently I grinded for a decent plague staff and started using it on my mage account, however, even though it's displayed that it's not supposed to do damage, the meteor spell still does a significant amount of damage. I don't have anything that gives an increase to spell damage, so why is the meteor spell with the plague staff still doing damage?

Also, if anyone knows exactly how the plague staff passive works, that information would also be appreciated.

 

Could you share your full build? That could help us better understand your first problem.

As for the Major ID, the way it works is that if you attack a mob, it will take the poison damage, and then "spread" that poison to nearby mobs, making them take poison damage as well. I believe that it eventually has a limit, either on damage or mob total, to prevent this from being ridiculously op.