Elder-Basilisk: Just remembered last night. The drow can use Faerie Fire on their opponent, which allows them to sneak attack in Darkness.
My DM and I were talking about Darkness last night. We're going to play as though the area were really dark. If there are only normal light sources around - torches, light spell, candles - then you can only see if you have low-light vision or darkvision. In the Underdark, humans and halflings are blind in a Darkness spell. If the spell is cast outside during the day, anyone can see through the darkness. In any case, everyone gets 20% concealment in the darkness. The spell implies that this is how it works (I guess???)
It's lame that the changes to the lighting rules don't seem to be playtested, BTW.