Hi, after a lot of testing I made this version of a zoo deck and I believe it is the strongest. I usually get quick legend with zoo decks every season but this season it took me a little bit longer because besides not having much time, I played different decks. When I reached rank 3 I started playing this zoo version and from there I reached legend with only couple losses. Also, it seems to be exceptionally good against secret paladin.
UPDATE: adding big game hunter for void terror and kezan for wolf is giving me better results, will update list if it keeps being like that.
My guide for beginner / intermediate players on how to reach legend (from my own experience):
The most important thing with this deck is to know when to trade and when to hit the face. To help with that decision, just try to always predict what will happen next 2 turns. Remember never to over-commit to trading, let your opponent do it. That's why we have all these taunts in deck, to buy us time to expand our board and put even more pressure while the opponent is worried about trading and stuff.
Never be afraid to life tap. But also, only do it if you have no minion to play. Life shouldn't matter much since with this deck you control the board, but to control the board you have to play minions whenever it's possible.
Also, keep in mind that sometimes you have to sacrifice your stronger minions on board to have upper hand in the following turns. Keep in mind that all the minions are expendable. Anyway, just practice!
Keep abusive sergeant only if you think he will make a difference in early game and help you trade. I usually keep 1 implosion, and I keep 1 power overwhelming only against a warrior and if I have egg as well. Otherwise I don't keep it. Keep eggs, spider, 1 mana drops, annoyotron if you have a coin or if no coin but no other 2 drops. Keep void caller if other 2 cards are 1 or 2 drops. Keep gang boss if you have things to play before turn 3. It's very hard to get a bad starting hand with this deck, and I see that as a big advantage. Keep void terror only if you have an egg and the opponent doesn't have a fast deck. Never keep owl (except vs hunter) and expensive minions. Against a warrior make sure you don't keep more than one 1-attack minion.
Also, against fast decks, don't over-commit to egg + void terror combo, it slows you down a lot. Against slow decks it's awesome but if you play turn 1 egg, turn 2 egg, turn 3 void terror against a tempo mage, it's game over, you lose. Always go for the fast start.
WARRIOR: most common are control and patron: for us control is easier matchup because even though it has more removal, it generally gives us more time until any they play any real threat to us. This is all about applying as much pressure every turn as possible. If you have egg + power overwhelming or egg + void terror combos use them as soon as you can. If you have flame imps and knife juggler play them right away even if they have fiery war axe. They still take 3 damage in the face and they use up one of their weapons and then we start playing bigger threats. Keep in mind they have whirlwind effects, so usually it's better to sacrifice some of the minions when trading with theirs than have everything on 1 health. Keep flooding the board, and don't worry about the brawl. You can always counter it with eggs or voidcallers.
DRUID: pretty much everyone is playing a combo druid. Here you want to keep 1 implosion in the starting hand if you get it. It will help you trade minions better. In early game it is very important to kill any minion they play and keep pressuring them as much as possible. When we get to mid game, if we have some taunts up we can afford not to trade, but also kill whenever it's possible. Most important thing here is to take advantage of all the minion buffs we have (abusive sergeant, wolf, dwarf, power overwhelming) in order to trade minions more efficiently. Don't worry about swipe, if they only have one, it shouldn't help them much.
PALADIN: against secret paladin we pretty much want to hit face as much as we can. Only trade minions if it will give us big advantage. Usually it's better to let them worry about trading, and we just keep hitting face and taunt up when possible. However, if they don't have avenge or redemption we can clear their board easily. On turn 6 when they play challenger we should be fine usually. Use weakest minion to activate noble sacrifice. After that you see exactly how much damage they can do to you and your minions since all the secret paladins run pretty much the same decklist, no surprises. According to that you decide if you want to kill challenger or just go face and set up lethal for next turn.
Against a midrange paladin we play completely different. We trade every minion (efficiently of course) so we maintain full board control and keep their board empty whenever possible. We should end up out-valuing them and pressuring them too much.
WARLOCK: against other zoo warlocks it's pretty straight forward. Just try to get the best possible start and board control, and when you see a good opportunity transform to full face tactic to finish them in a turn or two.
Against handlock just pressure as much as possible, and try to play gang boss, egg and voidcaller when you can because they are amazing against hellfire. When they play twilight drake kill it if you can. You can leave it alive if you have taunt up and egg ready. It is important to play around shadowflame. Keep them on 13 health unless you have lethal to avoid molten giants and finish them next turn. Shadowflame and molten giant are only scary things there but they are easy to play against.
PRIEST: This one is all about board control combined with face pressure. Keep their board empty so they don't get any surprise velen's chosen buffs or big holy nova value. Unless they get a perfect start it should be fairly easy for us to do this. Keep eggs unhatched most of the time to play around holy nova. If you get loatheb play him to counter lightbomb and set up lethal. Control priest is extremely easy matchup while dragon priest can be tougher depending on their start, but we have much more resources and if their hand isn't perfect from the start then we should be able to keep the board control and pressure.
SHAMAN: just kill all the totems all the time. Pretty much keep their board empty. Lightning storm can't do much to stop us, and I don't see any other real threat.
MAGE: there are 4 different standard types of mage decks around: freeze, duplicate/tauntheal, tempo and mech. The hardest is mech mage, other 3 we should beat most of the time. Not always of course.
Against mech mage we have to get the fastest start possible. Flame imps, jugglers, eggs with abusive sergeants, it all helps. It's important not to take too much damage in early game. We need to get board control against this deck and we will always end up doing it. However, problem is that if we do it too late and we take too much damage they will finish us with fireballs.
Tempo mage we can have only slightly slower start than mech mage. It's much easier because they can't do as much pressure to us in early game. This is all about board control. When they board is completely empty hit their face, if it's not then hit the minions.
Against freeze mage we have to do as much damage as possible in early game. There is no real threat to us until turn 5 when they do doomsayer + frost nova combo. We can avoid one of these if we have owl. It is important to always leave some space on board for doomguards and loatheb. Those are our most important minions here. We have to pop ice blocks without doomguard help, and use doomguard as a finisher. Loatheb is used to make the freeze mage pretty much skip a turn, which if done at the right time will win us the game. Always keep eggs unhatched and let them hatch them with blizzard / flamestrike / doomsayer.
Against duplicate/tauntheal mage just go face as much as possible. We should normally be able to pressure them too much until late game when their deck shines. This is easier than freeze mage because they can't freeze us!
HUNTER: this matchup is hard because of their secrets and potential knife juggler + unleash the hounds combo. Against facehunter always expect explosive trap even though sometimes it will be a bear trap. Just kill all their minions in early game and as soon as we taunt up (argus on imp gang boss preferably) we should start hitting their face with everything. We can play doomguard on turn 5 because they won't even try to kill him and we need as much damage as soon as possible.
Against midrange hunter it's pretty much the same as mentioned above but the only difference is that they will run some freeze traps and we want to make sure that we can offer it a good sacrifice, like little spider from haunted creeper deathrattle or little imp. Don't use hero power if you are under 20 health or so.
ROGUE: oil rogue is the most common rogue version, but against any rogue we have the same plan. Always keep their board empty, keep flooding our board, and keep egg / voidcaller / imp gang boss / haunted creeper to counter their blade furry.
This deck is also good at recovering / surviving board clear spells (consecrate, swipe, hellfire). Some faster zoo decks that are stronger in some other situations have bigger problem with that.
Power Overwhelming is a really strong card in zoo decks. You will either pop use it to help you with trading, or to summon nerubian or you will keep it as a finisher. It all depends on the situation. I believe that zoo deck shouldn't have more than 4 spells, and this spell, as well as implosion definitely deserve to have a spot.
Abusive Sergeant looks really bad on his own, but he really makes a difference so often, both in early and late game. He is only 1 mana drop so it's easy to fit him in the curve at any time and it helps you with board control a lot.
Flame Imp is very straight forward. It gives a lot of early game pressure which makes a lot of difference, and for late game 1 mana fits the curve and applies additional pressure. Amazing card. Don't worry about 3 damage to yourself.
Voidwalker is another minion that's good in any point of the game. In early game he can combo well with wolf or abusive to trade better and establish board control, and in late game it's a useful taunt. Very important in this deck.
Annoy-o-Tron is the card I put in instead of second haunted creeper in order to fit the meta better. It slows down the aggro decks and makes you establish board much better. It also blocks warrior weapons quite well. He is maybe even more useful in late game. Really made a difference for me. But running two of those would be too much, just like running 2 creepers is too much with this meta.
Dire Wolf Alpha helps you establish board control and his power grows with the number of minions you have on board. Keep him in the starting hand only if you see he will be useful, usually in combination with voidwalker.
Haunted Creeper is a really strong anti-aggro minion, but with current meta you can only afford to run one of those. There are many priests and warriors around and against those he is not the best. He is a 2 drop we need to fit our curve.
Ironbeak Owl is there because we need to have one silence, it helps in so many cases. Be smart about using it. Only keep it in the starting hand against a hunter.
Knife Juggler is just awesome. Just don't rely on his RNG unless you really have to. Just remember to never worry about combo with implosion. It doesn't matter much. Just play juggler whenever you can.
Nerubian Egg is one of the best zoo cards. He trades with other enemy minion because we activate him with one of the many activation cards we have in our deck and then we even summon a 4/4 which is really good in a zoo deck. So very often this will end up being traded for 2 or even 3 cards. Really strong.
Imp Gang Boss is a must have. He is pretty much the best defender of argus target, and he also summons little imps that we end up buffing and trading. He is also a 3 drop which we need for our curve. I don't recommend playing zoo without this card.
Void Terror is good to have because quite often he will end up being a really strong 3 mana minion with no downside. When you play him try to be as efficient as possible and always think of removals that the opponent has.
Imp-losion is such a great card for zoo. It kills a minion or at least helps you trade, and it summons little guys that can be buffed. This card is also a must have in a zoo deck.
Dark Iron Dwarf is extremely useful pretty much every time. 4/4 stats are huge for a zoo deck, and that buff helps you with board control. In this meta he is strong against warrior and priest decks, but anything else as well really. We only have space for one of these so we can keep a good curve.
Defender of Argus is by far the best card in this deck. Those taunts and buffs at the same time are so important and make a huge difference. However, I never keep him in the starting hand. He is a card that we draw and we own with it.
Voidcaller is in my opinion stronger than shredder in this meta. And since shredder is supposed to be the best 4-drop minion, then it's only logical to run voidcaller. We have 2 doomguards to combo with them. If he is silenced, the enemy will waste silence and you will still have a somewhat sticky 3/4 on board. And if he is not silenced then you can do wonders with him. He is initially slow, but with the momentum you get the next couple turns it definitely pays off. Just make sure you have solid board control.
Doomguard is another a definitely must have for zoo decks. There will be so many games when you will draw him as a finisher. Other times you will combine him with voidcaller which will also end up with you finishing the game. However, make sure you don't discard any useful cards unless you have to and it will bring you big advantage.
Loatheb is also really important to have. 5/5 is so strong in a zoo deck, and making enemy unable to cast spells for a turn will usually give you huge advantage and board control and enemy will never be able to recover from it. He is good in any deck, but in this deck he is even better!
Dr. Boom is simply OP, and in zoo we have even more synergy with boom bots. We need this as a lategame and if we play it on turn 7 we win. Don't worry about enemy BGH. If they play him that means they will fall behind because they will have less mana for other cards and we still keep our boom bots. If you are a new player, this should be the first card you craft. If you can't afford him yet, you can replace him with fearsome doomguard in this deck for now, but it's not nearly as good.
Feel free to ask any questions! I also don't mind being observed in my games, so if anyone thinks that can be helpful for them to learn this or any other deck feel free to add me.
I know that most of people reading this already know how to play zoo deck. But I know that for new players guides can be useful so they get some general idea how the deck works. So I hope this will help someone at least.