Good Job. A word of warning though, Cass decks are very expensive in terms of spirit when fully built and unfortunately outside of Abyssal Juggernaut, the other payoff cards are legendary (Ghost Azalea and Obliterate).
Also since you’re fairly new, Healing Mystic should be an auto 3 of in every deck you build. You would specifically need a reason to not run it. It’s a 2 mana 2/3 neutral minion that heals a target for 2 and it’s a core card you start with.
I would also take out Lug Ignis,Tethermancer and Shadow Nova and put in Hailstone Golem and Ephemeral Shroud. Shadow Nova is overcosted and tempo loss is normally pretty bad and the other cards just don’t have a good enough cost/effect ratio. Ephemeral Shroud gives your faction targeted dispel which is crucial since we don’t have any of our own.
If you stick with Abyssian in the long run outside of making one of each rare to unlock triple Sister Kelaino, the best card to make is 2 copies of Spectral Revenant as it’s our best faction defining card. Hopefully you can open the third.