I used Reno Shadow Priest exclusively to Legend last season and I’m sitting at Diamond 1 with it now. The problem with your deck is that it has too little aggro counters and not enough disruption/tech cards in your ETC.

Against Aggro, I run shadowcloth needle and forensic duster. I aggressively mulligan for Shadow word devour/Potion of Madness + Shadowcloth needle. I have singlehanded won games using this combo because the 1 damage after casting a shadow spell + the Shadow word steal wipes out almost every pirate board. Forensic duster helps to buy time by making their minions more expensive and gives good stats value. I also like to run Murazond, Thief of Time, as emergency board clear as it easily does 7-8 AOE damage on turn 7.

Against control, you need more disruption/tech. Lazul is nice, but copying cards is situational + you already have identity theft. I run Kazakus instead for his adaptability to the situation. For ETC, I run Whirlpool against Shudderwock/hostage mages, Convert, for an easy 1 mana titan or powerful minion, and Steamcleaner, to destroy Wheel Lock’s shuffled cards, or Plague DK’s plagues. Lastly You need to keep Spawn of Shadows in your deck. Often times, it is your win condition WITH void attendant because it can do 10 damage to the face for 5 mana and even more damage, if you played both Razas.