Mulligans
General Mulligans
Dead Ringer to ensure as much of your combo pieces get drawn immediately.
Northshire as a solid 1 drop that can compete for board and draw.
Spirit of the Dead, can be flexible if you know you are playing vs an aggro deck then the 3 health statline that can be buffed on turn 2/3 can win you early board presence as well as it reduces the chances of drawing it using your Meat Wagon which again helps your death rattle combo to take effect sooner.
Devilsaur Egg as a solid 3 drop and the main sauce of your board presence; your deck should hopefully contain enough egg activators and buff synergy that you should be able to draw it without having to mulligan for it.
Theory Craft for the next expansion, using the old breakfast priest which looked into the synergy between Meat Wagon and Devilsaur Egg combined with buffs to activate and create a minion heavy zoo priest. This next expansion provides this archetype with so many tools I am convinced this will see top tier play.
The big tools that create this archetype in this expansion are Arena Treasure Chest, Spirit of the Dead, Surrender to Madness, Mojomaster Zihi.
The synergy between Meat Wagon and Arena Treasure Chest is possibly the largest source of value in this deck in providing draw and value with both of these draws being made consistent in Dead Ringer as well as Twilight's Call which as a card is so strong in this deck you wish you can run 4 copies; hence the inclusion of Shadow Visions.
Important to note is the inclusions of Fungalmancer and Unidentified Elixir in that they both provide +2/+2 to their target so to use on a post Surrender to Madness but unbuffed 1 attack Meat Wagon would ensure that Meme Wagon still pulls your poten deathrattles. With Spirit of the Dead cycling cards into your deck also so you can continue to utilise your deck thinning and draw to maximum efficiency giving you the late game push you would need vs slower decks.
Without a doubt, I think the sheer value alone on this deck could cause it to see top tier play with the major concern being that there is an even stronger zoo deck that can out board control this one.