well, went to look at wow website at the talent calculator, and the archimonde's darkness spell is differente from what it is on live.
On live, give 2 charge of dark soul, and on calculator, it says enemy will take 25% damage you take for 8 secs, with a passive 5%
its going to change in wod or in a near patch?
http://us.battle.net/wow/en/tool/talent-calculator#V!