SoU Shadow Priest

It took me a whole two months, but I think I finally refined this deck.

Playstyle is still pretty much the same: similar to a Midrange deck. Swarm the board with tiny Deathrattle minions, or play defensively as you ping your opponents down. Get them low enough, and you can do up to 18 damage with Leeroy Jenkins and Wretched Reclaimer to finish them off.

Psychopomps can potentially resummon some powerful cards, such as Leeroy Jenkins or Zilliax, or can be used to just resummon a Deathrattle minion. Wretched Reclaimers can also be used to trigger your Deathrattles, to resummon a Reborn minion, or to truly steal your opponent's minions.

Now for Shadowform: The hero power lets you have a 2 damage (or 3 damage) ping each turn, which can actually be really helpful for either dealing with enemy minions, or pushing out that extra little bit of damage. With how low the health of the majority of the minions in this deck, there is never really a huge need to heal them, meaning that transitioning into Shadowform doesn't mean giving up an essential part of the deck.
Always remember that playing a second Shadowform refreshes your hero power, so you can use your 2 damage ping, then immediately refresh and use your 3 damage ping.
It may not be a Mind Blast, but it's something, at least.

Onto the updates:
After a little bit of experimentation, I've noticed that Piloted Reaper was a fantastic card to throw into the deck. Yep, you heard me right, Piloted Reaper's finally got its time to shine. Lost Spirit also became a pretty fun thing to include, giving your (hopefully) decently swarmed board of Deathrattles a small boost in attack. I have also taken out the Northshire Clerics in place of Loot Hoarders, as the former just lost any and all usefulness once you've transitioned into Shadowform. Shadowy Figure was a last minute decision to replace the two copies of Seance, as the latter felt both too slow and only really good to use on two cards in the deck.

Lastly on the list of the updates, I threw in two copies of Extra Arms because... well, I'm not sure why I didn't include them in the first place, seeing how this is the type of deck that all those arms thrive in.

And of course, a visual guide on the finisher:

If you don't own Leeroy Jenkins, a nice budget option is Reckless Rocketeer. While not the flashiest minion in the world, it allows you to have a 15 damage finisher while still being within the confines of 10 mana. Just remember to attack before Reclaiming the minion.