Just for fun wild deck, not really competitive :)

How to play:

The first goal is to complete the quest as fast as possible, there's 11 low cost deathrattle minions for this.

When you turn into Shadowreaper Anduin, use the remaining low cost cards to fuel your hero power.

For the late game, Archbishop Benedictus will provide more options and replenish the deck as you should draw quite a few cards with Dead Ringer, Loot Hoarder and Bloodmage Thalnos (plus their rezzes through Twilight's Call).

Explosive Sheep is nice to deal with aggro, can be triggered in the same turn with damage dealing spells.

Mulligan:

Deathrattles minions, especially the card-drawing ones.

Twilight's Call or Shadow Visions to fetch it.

Replacements:

The deathrattles package is required to provide consistency, so they're pretty much mandatory.

Chameleos and (not tested yet) Madame Lazul are just here to add flavor to the deck, they can be replaced by cards of your choice (a second Seance for example). Minions are best though since they do not dilute your spell pool too much for Shadow Visions to offer good choices.

Excavated Evil can be exchange with Mass Hysteria

Dragonfire Potion can be exchange with Lightbomb