vs aggro: Voidwalker
when you have coin: Dire Wolf Alpha (it's a good turn 2 play when you played two 1-drops on turn one)
Cards that might be included:
Why would you play new 'trashy' cards?
Grim Rally - usually you will sacrifice 1/1 or 1/2 minion to buff other stuff. Interesting thing about it is that it might be considered as a charge dmg as long as you have minions on board that can attack. This means a lot of value and small sacrifice specially because Zoo runs a lot of little creatures (tokens)
Spirit of the Bat - terrible card in terms of tempo but when you will play this later when you have to trade into taunt minion or just trade to gain board control you will also buff sth in your hand (just keep doubling imp or saronite chaing gang and make sure to have small amount of minion to increase the odds of targeting one of those cards). It also works with buffs because it will make it harder to kill and maybe you can get more 'buffs'
Scarab Egg - do you remember Nerubian Egg? that card was great in zoo. This is slightly worse version of it but still you gain a lot of value out from it and it synergies with Dire Wolf Alpha or Spirit of the Bat