Hearthpwn

Hello and welcome to my Rattle zoo version. (Still under serious testing)

I have focused to get lot of valuable Deathrattle minions to buff Undertaker for good trades, I also choose to test Zombie Chow due to it's big early game pressure.

Mulligan

I would mulligan everything above 2 mana drop.
If you have coin + Undertaker in start then you can keep Harvest Golem, due to Undertaker round 1, coin + harvest golem round 2 will give you a big headstart.
Also this is where Zombie Chow shines, if you get him early game, since you want to establish board control and not aggro, he will be good to trade with Abusive sergeant buff, against possible 4 or 3 life creatures. 

Strategy

Main focus on this deck is not aggro, it's to establish board control and do safe valuable trades with example Zombie Chow and to buff undertaker. BUT dont focus on buffing Undertaker if you dont have him early game due to card draw, still Chow is really strong in my opinion alone to trade early game minions.

It's important to know to active eggs when they come out, this you can do several ways, either with Abusive Sergeant, Shattered Sun Cleric, Sunfury Protector, Dire Wolf Alpha or Void Terror.
This make eggs easier to play and have a possible good effect to buff Undertakers.

Mindset behind eggs and why I have alot of cards to activate them, is due to mindgames, when en egg is played on field players tend to either deal with siliences and/or fear to use aoe due to it's strong deathrattle effect and if they dont you activate them and they become hazardous.

End Comments

I Have enjoyed a lot of games with this version of zoo and still think a lot can change so feel free to comment and give hints/tips or just ask questions, there are no stupid questions! :D

I have updated this deck with 2x Shade of Naxxramas at the moment there is many hunters running with flare, but since warlocks do not go with so many stealth minions the risk is small to encounter that.

I also feel that Shade fits quite good with this deck, since you play around board control and not aggro, so you can have other minions trade and protect shade to get bigger and avoiding many aoes.