@JeremyECrawford Fog Cloud=heavily obscured. I ranged attack enemy in Cloud from outside Cloud. Adv or Adv/Dadv canceling each other out?
— Frederik Forger (@forger_f) April 18, 2016
Advantage and disadvantage always cancel each other. #DnD https://t.co/LFyQft5YG5
— Jeremy Crawford (@JeremyECrawford) April 22, 2016
if neither have vision that can penetrate the cloud they are both practically invisible to each other – both have disadvantage against each other.
The advantage gained from the ‘blinded’ condition assumes that you can see the target but it can’t see you. ( which does not apply here )