Mulligans
General Mulligans
Cleric is the best card in the deck in every matchup, but know that you often want to save it until you can guarantee draws in more control matchups. Stonehill Defender is great for curving out against slower decks and deadening early aggression and protecting Clerics. And of course, Shield is always good to put on a card to make mana more efficient and improve trades. All of these cards should be kept against aggro, control, midrange or combo.
Aggro Mulligans
Duskbreaker can also be kept more generally when you have access to a dragon or otherwise a good hand, but you always want it if any kind of aggression is possible. Spirit Lash or Shadow Visions should be kept against Paladin, but not often against Rogue, and definitely not against Mage. It's best used for the healing there, so we want as many copies as possible in our deck to maximise the amount we can achieve. Shadow Visions is obviously only really good if you can't find the other two.
Midrange Mulligans
By Midrange, I mean Spiteful Druid/Priest, which is why we're keeping Death and Acolyte and Shadow Visions if you don't manage either. There's just a lot of really good cards in these matchups, and you can't draw them all, but you only need one or two of them. Just try and keep to the curve but save your clerics until you can draw from them.
Control Mulligans
Shadow Visions pulls a lot of legwork for finding the spells in our deck, so we're really mulliganning for the draw and the minions in the deck against control. Don't make the mistake of keeping Mass Dispel against Cubelock; we would rather get extra copies with Shadow Visions so we can push through the taunts. For that matter, you may want to hold off on Shadow Visions turn 2, see if you can improve your odds of getting extra copies of the spell you want by drawing a little first through the other spells.
Currently running even on wins and losses at rank 10. Yes, laugh all you want, but this is my first season playing ranked hearthstone, so you know. In game I’m currently running a “budget” version that swaps Thalnos, Mass Dispel and the stonehills for two Wild Pyros + Circle of Healing, but it’s changing a lot. Despite that, I feel this deck has potential as an archetype with a strong matchup against both aggro and control, and better than all the existing priest decks.
Gameplan: Play Coffin Crasher, Cube it pulling another large deathrattle minion, Vivid Nightmare the Cube, then kill your opponent with a large and sticky board. Or, if their board clear is too strong, do exactly what Cubelock does, pull out a Bone Drake on your turn and then Cube that to generate a huge number of threats. Pulling out Rotten Applebaum and Obsidian Statue sandbag aggro and tempo decks.
Northshire Cleric + Power Word: Shield: Vital in all Priest decks, obviously, but this deck especially needs draw. I’d love to fit in Circle of Healing and Wild Pyromancer in the final list because Cubing Coffin Crashers pull so many, many cards from your hand.
Bloodmage Thalnos: Why Thalnos in a deck with one spell that does damage? Because that spell has Lifesteal. It’s not difficult to use it to heal for 10+ health against decks with reach like Combo Priest and Tempo/Crow Mage, and additionally it draws you a card which is always good as mentioned above. If you really like healing, try tripling that heal with Vivid Nightmare. Careful Coffin Crasher doesn’t pull it, but if that’s likely then it’s probably not a matchup where you care.
Shadow Visions + Spirit Lash: Spirit Lash obviously destroys Paladin and it’s the number 1 reason I think this deck is better than Spiteful Priest, but the more I play the more I’m relying on this card in all matchups. It’s not difficult to use it to heal for 10+ health against decks like Combo Priest and it’s interaction with Thalnos because of how sticky your board is, which is why this deck doesn’t have Divine Hymn, and it lets you pop Vivid Nightmare Cubes to escape Hex/Polymorph/Silence effects if your list isn’t running Wild Pyro (which is another reason to run that card).
Shadow Word: Death: Entirely for Spiteful Summoner decks, but also makes Hench-Clan Thug sad. Just a good card to have access to.
Stonehill Defender: The reason this deck has an even better matchup against aggro and tempo decks than other control priests, thanks to class offering boosts (Obsidian Statue and Tortollan Shellraiser) and a naturally large number of deathrattle taunts in Standard this card does double duty increasing the stuff that Coffin Crasher can pull making it great in control matchups too. It can even find Primordial Drake to turn on dragon synergy. Really good.
Twilight Acolyte: Makes Mountain Giants and Lich Kings and Tyrantuses manageable. Extra good in this deck because of how minion focused it is, and better than in Lady In White/Keleseth decks because it doesn’t donate extra attack to your opponents.
Vivid Nightmare: Makes this deck tick. The reason we want this instead of Mirage Caller is because it can be searched with Shadow Visions for ultra-value and because 6/1s or 4/1s are far better late game than a 2/3 + 1/1. Don’t be afraid to use it on just about anything though, your plan is to beat your opponent in the face and you can heal up what you use it on with your hero power.
Duskbreaker + Twilight Drake: duh. It’s sometimes worth saving a dragon that you can play just to keep this card active. I’ve used it to break open my own cubes before.
Carnivorous Cube: You can pull this card with Coffin Crasher, which is often why you want to Cube it before that happens, but this deck has a high enough density of deathrattle minions that it’s rare and even if it does happen, that’s still basically a better Cairne Bloodhoof (a card that would also be nice in this deck).
Rotten Applebaum: Makes Odd Rogue and Tempo Mage so very, very sad. It’s still the worst deathrattle minion we can pull, but it keeps the density up is good for the curve. Rotten Applebaum into Vivid Nightmare Spirit Lash trade against Mage for a 12 health or more swing is brutal. After Stonehill into Duskbreaker into this most aggressive decks have to settle into the long-haul which we will win.
Bone Drake: Similar to Applebaum, it’s not a great deathrattle minion, but it’s also a dragon, it makes a bunch of stuff that control decks have to remove, it’s large enough to be a threat after they’ve already killed Coffin Crasher.
Coffin Crasher: OK, I’ve already said plenty about this card. Obviously when you draw it it completely changes how you play, as you can rely on it saving 5 or more mana on another card so your better off value trading and healing instead to maximise that value. Tell you what too, 6/5 is a way better statline than Possessed Lackey’s 2/2. You’re really trying to beat your opponent down with this deck.
Obsidian Statue: My Voidlord, if Voidlord killed things as well as ruined every aggro deck. Cheating this out from a Coffin Crasher feels just as good as Possessed Lackey, and if you do then trading into something and then cubing this to kill another thing usually has your opponents reaching for the bottom right.
What Feels Bad And What Feels Good: This deck is excellent at getting to turn 6 with excellent clear and plenty of taunts and heal and once you have the game is on lock-down in a way that feels very Cubelock-y. However, it’s not nearly as susceptible to Spellbreaker (surprisingly) because a 6/5 Coffin Crasher is way better against midrange than a 2/2 Possessed Lackey when silenced. This gives this deck a definite “safe” feeling that Cubelock doesn’t have, where you’re happy to get beaten up a bit early on (I often do nothing but heal turns 1 to 3) which means you can be a lot more reserved with your board clears and use them when they reload the board. The upshot of this is that this deck destroys more mid-range aggression from Even/Odd Paladin that rely on Spellbreaker/Ironbeak Owl against Cubelock as well as traditionally high-aggression decks like Odd Rogue/Hunter which lose from all the taunts. The bad news is how much you love drawing certain cards in all sorts of matchups; Northshire, Spirit Lash, Duskbreaker, Vivid Nightmare, Cube, Coffin Crasher are all cards that I’ve really wanted in my hand at some point or another. That last one is particularly problematic; the hand fills up with too much trash when you can’t find it and you empty your hand too quickly when you can. Careful play and greedy drawing help, but there’s so many directions you could take this deck I’d love to hear your ideas and tests.