I remember considering Nightmare in exactly one deck, but the deck never made it due to suffering greatly from denial, and Nightmare was just not worth wasting the card space. Even with the perfect target there's better cards to think of than nightmare to put in.
Overall, Nightmare isn't worth the card space most of the time. I remember talk in chat that situational stuff gets healing (luciferin, purify, possibly sanctuary) so letting Nightmare do just that might help, since the effect as is is insufficient, regardless of the card that fills the opponents' hand. Then again, I don't see luci getting used that much more.
A different suggestion would be to enhance the effect, I heard stuff like put a lot of cards on top of the opponents' deck, and it was considered OP, but what about adding just one? That would double the draw denial it gives and makes it worthwhile since you waste one turn, and your opponent loses two, right now you're delaying both sides at the cost of quanta and that the effect actually benifits your opponent in some cases. Ghost of the past is a step in the right direction, but that alone won't make the card good.