Hello, my name is Tox. I practically only do Custom cards stuff, but I accidentally ended up at a somewhat high Legend rank, with a card that I think is somewhat underrated.

The deck is built with the idea of consistency in mind. Practically all the cards in the deck are playable at any point and board state, and therefore makes you able to push, regardless of what is in your hand.

Mulligan:

Instead of being silly, and giving you a list to keep in every situation, then I'll simply say that you should keep cards that synergize well together, and forms a good curve.

This includes a 1-2-3 Drop without being on Coin or 1-3-3 with Coin. EVIL Recruiter can be a keep on Coin if you have Sinister Deal aswell. I likewise wouldn't keep EVIL Genius, unless I have either Murmy and/or Mecharoo in my opening hand, but it is not great for your tempo if you have to sacrifice any other 1-drop.

Matchups:

Quest Druid: Play stuff. If you can coin out History Buff, you win the game immediately. This is the sole best matchup.

Combo Priest: Hard mulligan for a very aggressive start, including Flame Imp and Spirit Bomb. If they get ahead, you're most of the time done. Remember that their old real sort of board clear is Wild Pyromancer. You want to clear absolutely everything, and you need to prioritize High Priest Amet above everything else. This matchup is about even.

Mages, Including Big Spell Mage, Combo Mage, and Highlander Mage: They pretend to be different decks, but they're fooling no-one! They're all favored matchups (especially Highlander Mage), but you need to be very wary of their board clears and freeze spells, alongside Doomsayer. Highlander mage can only have 2 board Freezes, and you'll generally want to go full ham after one of them have been revealed. Zoo generally wants to fight for the board, but in this particular matchup, you need to push the face fast, as they get you in the long run.

Control Warrior: Most of your opponent's cards are irrelevant, with the exception of Brawl and Warpath. According to my stats, I have a somewhat better matchup against Warrior than the standard Zoo lists, which is likely because of the snowbally nature of History Buff. Keeping Dark Pharaoh Tekahn can also be a good idea.

Tempo Warrior: In all other matchups, your Health is not really a thing you want to worry about. Tempo Warrior is the only exception. If you can remain somewhat healthy, and get a 1-Drop at the start, then it's a really easy matchup. Their most explosive tempo plays requires them to have damage minions, so trade as efficiently as possible.

Murloc Paladin: This matchup varies a lot. You want a very explosive start, alongside preferably Knife Juggler to snowball. If they don't draw their combo, it's a laughable matchup, but the only way you can defeat them if they have their combo is by having a very resilient board early on.

Quest Shaman: Quest Shaman practically has 1-Aoe, and that is Sandstorm Elemental. Be wary of that when you build you board, but else way, go full ham. Their removal often sucks early on, so you can often get a Knife Juggler or a History Buff running, which they absolutely despise.

Card Choices:

The deck includes a bunch of cards, that is practically mandatory if you actually want to play Zoo-lock. Including Flame Imp, Voidwalker, Dire Wolf Alpha, the whole Lackey Package, and the self-damage package excluding Spirit Bomb.

Murmy and Mecharoo: They're in the deck for the same reason. They're the best target on turn 2 for EVIL Genius at best, and at worst, they're just pretty efficient 1-drops, that are pretty sticky.

Spirit Bomb: One of the highest Tempo cards that Zoo has. You can often murder a 1-4 Cost minion at the cost of a single Mana, while it has excellent synergy with Vulture. The card is absolutely crucial against Combo Priest and is also really strong in the mirror and against Tempo Warrior.

[Hearthstone Card (Soularium) Not Found]: You'll likely notice that the deck runs really quickly out of cards in hand, and around turn 6-7 this helps either digging for Leeroy or Tekhan, or allows you to play several cards efficiently, despite having a practically empty hand.

Knife Juggler: This is your earliest true snowball card. If you get ahead against another Tempo deck, this lad can absolutely win the game with his juggles.

History Buff: Oh man, I have a lot of love for this card. This is the card that lets you win the matchups that you normally shouldn't win. If you get ahead against the likes of Quest Druid, Quest Shaman, Control Warrior or any variety of Mage, this card allows you to play one threat after another, despite not changing your gameplay whatsoever. Keeping him on Coin alongside a 1-Drop can be absolutely devasting against the slower decks.

Leeroy Jenkins: Some people don't play Leeroy in their Zoo decks. Those people are wrong. It also has excellent synergy with History Buff, where you sometimes get them with a 12-8 Leeroy. 

Replacements:

[Hearthstone Card (Crystalizer) Not Found]: Crystalizer is a decent fit for this deck. I find it rather awkward in the deck, except in combination with Vulture, as it doesn't trade that well, nor does it protect your other stuff. Currently looking at winrates, this could replace either Mecharoo and/or Murmy.

Sea Giant: Sea Giant is the likely the most controversial exclusion from this deck, and is a strong card in some very specific matchups. The biggest problem the card suffers from is how much it can clock up your hand, especially against the likes of Combo Priest and Control Warrior, where you need every single card to matter. If you want to play with Sea Giant, I recommend using the Egg+Grim Rally version instead of this deck.

Scarab Egg and Serpent Egg: As with Sea Giant above, These cards suffer from being "slow" compared to most other cards in the Zoo-deck. They also require very specific cards to do ANYTHING, which decreases your consistency. Again, if you want to use eggs, I recommend playing Sea Giant and Grim Rally aswell.

Grim Rally: See above. Also, if you're behind or about even, this is a dead card. Dead cards in Zoo means lost games.

Plague of Flames: Plague of Flames is a really strong card in very specific matchups, specifically against Combo Priest and all types of Mage. My biggest boggle with it, is how often it is a dead card, which slows you down quite a bit.

Arch-Villain Rafaam: Practically interchangeable with Tekahn. Both cards do about the same, which is putting a ton of value into your deck. Rafaam is somewhat better in very long games, while Tekahn is a lot faster. You can play both if you want to be really greedy, but i wouldn't recommend it. Again, cards that can't be played in almost any situation harms the consistency of Zoo.

Carpet: It has 1-Attack. For 3 Mana. That ain't killing any Warriors.

Proof of Rank, in case mods are evil.