The goal of this deck is to control the board with Auchenai Soulpriest + Circle of Healing/Regenerate, Bloodmage Thalnos + Spirit Lash and other removals. Then go into late game with a damaging hero power for control and attrition. Then finish off with a few HPs to face in combination with ressed minions.
Survive until you can res enough pieces to use your HP to either heal more or finish off your opponent. The quest is just here as an additional survival bonus, since you will be healing for at least 10 turns straight. If you do not have the quest, just sub a 2nd Mass Hysteria.
Additionally, Catrina Muerte is in the deck as a late game value card. If people keep killing or transforming your stuff, try to res her, and you will automatically gain your HP upgrade cards like Prophet Velen and Clockwork Automaton, if any of them died, eventually.
Alternatively, you can hope for some doubles from other res cards to control or finish the game.
Noteworthy combos are done with things like HP refreshers with one or two doublers on board. There are 3 options:
Normal form: Wait till your quest is complete and get some HP doublers on board, then use a surprise Auchenai to make use of your 3 *heal* HP for surprise damage to face (they will usually not expect an Auchenai, but only worry about your '16 healing' potential.
Shadow form: You can use 2nd Shadowform (if you've upgraded it once already via a 2nd copy from Shadow Visions before). Do 2 dmg * modifier with your first HP, play 2nd Shadowform, deal 3 dmg * modifier with your HP. I only added 1 copy due to lack of space and because it is often a dead card early in game against aggro.
Anduin form (your soft-OTK package): You can just HP, card, HP, ad mori. You can even use the 2nd Clockwork Automaton from hand to refresh Anduin HP for a 2nd more powerful shot to face. The most powerful combo is Vivid Nightmare on a double, to refresh HP and get a doubler. You can do this two times (The Dream) for 3 HPs and exponential dmg. For example: You have 1 Automaton or Velen in play. You do: HP for 4 dmg, Vivid Nightmare, HP for 8, Vivid Nightmare, HP for 16. That's 28 dmg (soft-OTK) with 2 cards and one minion in play (which can also deal 4 dmg if there are no taunts).
Easiest mulligan is: Auchenai Soulpriest+ Circle of Healing and/or Shadow Visions (for more flexibility)/Regenerate (if you suspect aggro and also mulligan quest for this). Alternatively, Bloodmage Thalnos + Spirit Lash and/or Shadow Visions are also a good keep.
Board control is everything, but do use your health as a resource, just keep in mind what they can do to kill you next turn if you are below 15 or so (bloodlust, everyfin, etc.) Third card is usually quest, unless you ditch it for survival tools if you are 100 % you are facing aggro.