--Core Card Stuff--
1M - Holy Smite/PW: Shield Usually when people run either of these, they run two of them, but I prefer just one of both right now. PW:Shield is a great cycle card that impacts the board for efficient trades, while Holy Smite is good for picking off minions just out of reach, or along with Pyromancer to handle some pesky minions.I don't run two Shields because drawing into two shields against face can be ugly, and smite is pretty much never a dead card.
1M - Northsire Cleric x2 & Zombie Chow This is a bit of a hedge. Zombie Chow is an excellent board control card, and Northshire is excellent card draw and also has the surprise factor of a Velen's Chosen combo that outright wins games sometimes. Cleric can float in your hand for quite a while against some face decks, but it's a strong turn one play against others (like Hunter, if you have a smite in hand). I like two Clerics because it allows me to more consistently draw cards against slower decks, and I like the presence of Zombie Chow but don't want to remove a card for a second one. It might be better to run two Chows and one Cleric, but I find Cleric more useful to draw into than a Chow after turn 1. You pretty much don't want to drop a Cleric down in most matchups until you can guarantee yourself at least one card draw from it, with the exception being if you have the coin and Velen's waiting in the wings for a surprise trade on a 3-2 drop.
2M - Wild Pyromancer Pyro isn't the greatest in this deck, but it has its big moments and it's a card you love to see in your hand when you go second with the coin against rush decks. It really can help you out. Against beefier decks, this is nice to hold for a Holy Nova combo for a 3-health wipe.
2M - Shrinkmeister x2 Everyone knows the beauty of Shrinkmeister at this point, and there's really nothing different about it in this deck, except that you want to make sure you have a very acute awareness of the types of decks you're facing and when the right time to use them is. If you're playing against Handlock for example, you don't want to just plop this down on turn two. You'll usually want to use it to steal a Twilight Drake if you can. Most of the time however I'll use this card at the first opportunity to get an efficient trade on the board. Stealing larger things is nice, but controlling the board with free trades is just as good.
2M - Shadow Word: Pain Of all the cards, I think having only one Pain is probably the most questionable decision, and if someone wanted to remove something like Bomber for a second Pain I wouldn't be too opposed. Pain works extremely well Shrinkmeisters and can help you deal with those tricky 4-attack minions. This is also a useful card to have to slow down face decks. Currently, I've decided I'd rather have another body on the board and make trades from there, than take the guaranteed 1-for-1 of Pain. Having at least one is nice, and two might be be better, but for now I'm just running one in favor of another body.
3M - Earthen Ring Farseer This card is almost always used to keep efficient trades on the board. Rarely do you want to heal yourself except in dire situations with little else to play. Healing up a cabal or a Belcher after a trade is the ideal scenario.
3M - Dark Cultist x2 One of the best 3 drops in the game, so pretty much required here. These cards are efficient and should be played even if you don't have a good way to get the buff. When you do manage to pick up the buff however, it can snowball in your favor quickly.
3M - Thoughtsteal Only one thoughtsteal, which is practically heresy for a Priest deck, but I'll say my peace. Against much of the face decks you'll find on ladder, thoughtsteal can be a weak card. Rarely against rush decks do you have the time to thoughtsteal unless you already have decent board control, at which point you should already be favored. Most of the crap you thoughtsteal from rush decks are weeny cards, and the risk of starting the game with two thoughtsteals in your hand is just too high for me to run more than one right now. Against mid-late decks thoughtsteal is insanely good, and it can be a win-more card against rush decks, but running more than one I feel is too risky in the event that you draw both early against face decks.
3M - Velen's Chosen I was running two early on, but I found two to be too clunky for this type of deck. Essentially, you only want to use this card to trade up, in a scenario where your buffed card doesn't die for free on the next turn. You rarely ever want to buff a minion unless it's to trade efficiently and allow it to survive. This way, in the worst case scenario, you kill one minion with it, and then they have to spend at least one card to deal with it, and you're squared up at 2 cards for 2 (minion+buff for minion killed + response card). More often than not though, this card snowballs and you get much better than a 2 for 2 trade.
3M - Shadow Word: Death x2 You pretty much have to run two deaths here. While you can trade up to higher-level minions decently well with various buffs and damage, you won't be able to reach the really big boys. This is also a great card to have in hand against Floating Watchers, Fel Reavers, and other big business that finds its way into faster decks. Deathx2 is essential.
4M - Shadow Madness Only one Shadow Madness. Great card, would love to run two, but I feel like two is often too clunky. You can probably make a good case to include a second one over another card, but you already have 12 cards at 4 mana or higher, and again, sometimes drawing both can murder you. Shadow Madness can slow down the rush but it's at its best when you already have minions on the board to take advantage afterward. Opening up the extra slot for a minion I think is better. This also acts as a nice way to reclaim the board when you don't have it.
4M - Dark Iron Dwarf x2 I used to run Yetis here, but Dark Iron Dwarfs are just much better because they allow you to trade up with minions you steal, or with lesser minions come turn 4/5 and you need to remove a Yeti with your 3-2 on board. The ability to jump levels in damage can't be overstated in a deck that can't win unless it trades efficiently.
5M - Sludge Belcher x2 Pretty standard. Useful card against almost any deck type, and can help you survive well against face decks (although they usually have an answer to the first one).
5M - Holy Nova Only one Holy Nova, as I used the second slot for Lightbomb, which gives more flexibility I believe by having one of both. It also curves out a bit better this way, as in super-dire situations you can Holy Nova turn 5 to clear half a board, then Lightbomb on 6 to clear the rest. More often than not though, you'll use Holy Nova while you already have minions on the board to strengthen your board control, and Lightbomb as a means to deal with heavy threats and take back the board.
6M - Lightbomb Lightbomb is an incredibly good card for this deck, in particular because it won't actually kill anything in your deck that matters outside of Dark Iron Dwarf. Ideally this card is played to regain the board if you ever lose it, or after you've baited an opponent into filling it. Lightbomb might seem like a not-so-great card against rush decks, but there's a decent amount of ways cards between turns 1 and 6 to stall and get a Lightbomb out if you really need it against such decks. Against more big decks like Handlock, this is a game-winning card.
6M - Black Knight Black Knight just gets value in almost every game it is drawn. A lot of rush decks gain time to refuel around turn six if they draw into a taunt to protect their minions, and against control you will pretty much always have a strong target for it. Pretty much the only downside to Black Knight is not actually drawing it when you need it, but it usually gets its value in a big way. This is also nice because you only have one Pain to deal with double belchers which many decks run, so a pain + blackknight handles things nicely.
10M - Mind Control Just one Mind Control, but it's often enough. Important swing card for late game or to kill the final fumes left in a face deck. There's just too much face though to run more than one of these right now I feel.