I have been playing this mono shadow deck for a long time, updating it from time to time. Posting it today as per a Reddit request. A lot of fun.
I use it mostly on Masters. I would not use it on Diamond II and Diamond I.
Work best against Justice decks and Big units decks (like Big praxis),
Works bad against Fire aggro decks, specially against Skycrag, and of course it is bad against heavy spells decks.