Short & sweet, Zombies
Objective:
Overwhelm enemy with little zombies as quickly as possible. Preferably, we start generating zombies the previous turn.
Who am I? Long time hearthstone player that has converted to GU. Am currently sitting around Diamond rank, for what it is worth. This deck is not conceptually very difficult, so I will try to do it justice.
Game plan & main cards:
This whole deck revolves around two key cards, our zombie generators: Cursed Obelisk and Necroscepter. These cards will continue to generate value while they stay in play, and can easily snowball, especially Necroscepter. This deck relies on frenzy-synergies, which means you will have to make sure to hit the enemy hero each turn (hero power useful here). This is because playing weapon removal is not very popular in the lower ranks, and also a reason why this deck becomes weaker nearing mythic. You will use these zombies to sustain your health, create more zombies, which in turn sustain your health... and you get where this is going. You additionally have another win condition in Corpse Explosion, where you often get to deal 15 damage by exploding your own zombies, which is super fun.
Other essential cards:
Blight bomb - Overpowered card, no reason to exclude it. Shines going second, not much more to say.
Netherswarm Lord - Now this guy is a total bro to your zombies, and zombie-like friends. Buffs nethers +1/1 each turn, and draws a card. Another must-have for a competitive deck. It also comes with a hidden passive of frontline, as the opponent cannot afford to not take it out.
Fickle Cambodian - Insane synergies with losing and gaining health, which we do a lot. I would include another one in my deck if I had it, but they are crazy expensive. Not necessary, but very good. Works well with brimstone, and of course, your hero power.
Rest of the cards, shortly:
Undead Roach, decent body which comes back sometimes. Void Banshee is a big body, and serves the same purpose as Netherswarm Lord, to be a big body. Voracious Fiend is a nice two drop which spawns a zombie, which can be super clutch to get your frenzy for a turn 2/3 Obelisk/Scepter.
Vanguard Axewoman is a nice 2/2 body for 1 mana which is useful going second. Eldritch Demonologist I am still experimenting with, but it pulls Vampiric Skull from your deck, which is a 6 mana 6/6 that summons your Obelisk back. Seems decent. Guild enforcer protects us against aggro decks.
Void Flash, Ray of Disintegration and Blackblood Blast are all different types of removal which come in handy to get rid of pesky, big, frontline creatures. Blackblood Blast lets us reset the board, and try again at times where there would be no other way to win.
Mana & Sanctum:
Without going too deep into this, with this deck you will want to pay attention to the sanctum, because not only do your zombies give the opponent less favour with the scepter equipped, but the sanctum is also the only place many people will get weapon removal. If you can, make sure to buy the weapon removal first, so that they don't use it on you. 13 favour is the cost of removing your scepter, just remember.
Concerning mana, this is especially important going second. Remember that you have the opportunity to play a 2-cost, 3-cost and 4-cost minions on your first three turns, if you wish. This often means coining out a two drop, and then your obelisk/scepter on the next turn.
Mulligan:
We mulligan hard for our two key cards. Depending on the match up you would consider keeping keeping any of the lower cost creatures, as well as perhaps picking up a blight bomb to deal with annoying creatures. As mentioned previously, vanguard axewoman is good going second.
Ideally, we are looking for not only our key cards, but an effective way in which to play them. A classic example of this would be this hand. If our opponent does not immediately kill our 2/2, we hit their face, get frenzy, and play our obelisk/scepter, and start rolling out the value. A key thing for this deck is use of mana: consider also the fact that you can use a mana crystal to hero power, and thus get frenzy off without having to hit them yourself.
| Going first | Going second |
|---|---|
| Scepter | Scepter |
| Obelisk | Obelisk |
| Undead Roach | Axewoman |
| Void Banshee | Blight Bomb |
| Voracious Fiend | Undead Roach |
Remarks on specific match-ups you will face on ladder
Big beast nature:
be careful of the broccolis, a.k.a. 1-mana zombie removers. These will stay up and make your life living hell. Mulligan for a Void Banshee, and try to get your scepter making zombies quickly. Not conceptually very difficult to play against.
Aggro war:
this deck will attempt to destroy you very quickly. Luckily, playing against this deck is fairly straight forward. Do not be afraid to drop to low health, if it means that you will get new zombies, as you want to clear off the zombies before the next wave spawns in any case. They will either destroy you, or run out of power slowly.
Final remarks:
Try this deck out and let me know what you think! This is my first post, so hello to everyone on Hive and the GU community in general!
Thanks to 
-yeetmaster