EDIT: I have since come to realize that although this deck has a plan (specified below) it doesn't really have a strong win condition. Although I really enjoy this deck and think it has potential, I think this iteration just isn't good enough. I'll try to keep working on it though.
As always, disclaimer, I am not a master deck builder. I just like to build custom decks that I have never seen before. If you've been paying attention to my decks you know by now that I have a deep love of Ephemeral Wisp and many other odd cards. This is a deck custom made for Ephemeral Wisp and it is actually pretty powerful when it works correctly. The basic idea is to build up incredibly powerful ephemeral wisps using Xenan Cultist, hopefully with killer, and constantly sacrifice them for the advantage that comes from other cards in the deck. Sacrificing, hopefully E wisp, with Devours and Direwood Prowlers allow the deck to become stronger and constantly draw cards in order to have more answers and options. The deck can also work when you don't draw E Wisp as there are other expendable units for sacrifice. Some other card considerations for this deck are Dawn Walkers, Vara, more Dark Returns, and potentially Copper Conduit. I am also unsure if Azindel and his gift are necessary in this deck. All in all, there are probably a lot of ways to tune this deck and make it better but this is the first iteration I came up with. Have fun with the deck concept and let me know what you think of it/what improvements could be made in the comments, thanks :)