Ok, I am sorry for the lower quality guide against but before I start I would just like to point out a few changes you can make to this deck if you want.

Basically, you can take out the Former Champ and put in a board wipe card like Lightning Stormor Hagatha's Scheme if you want a slightly slower way of playing the deck and you can put in Big Bad Voodoo for the Likkim and EVIL Cable Rat if you so choose although these have some nice synergies in the deck and all of these cards are totally interchangeable and you can have any mixture of them you want.

Gameplay:

Mulligans: Keep the early murlocs for some pressure and value at the beginning of the game so you don't get blown out, but they are also good options for later if you draw them later in the game as well. Into Aggro keeping overload cards and a Thunderhead to help you regain control on turns 4 and 5 would be a nice keep as well but a little risky cause it takes some time to get to that point. You also might want to keep a Zilliax because he is such an efficient form of removal for a lot of smaller aggro minions. Into Control, you want to keep the bigger minions and save the Murlocs for later in the game for added value from either Hagatha the Witch or the Underbelly Angler which gets you value later in the game. You want to keep combo cards so you can do it later in the game as well (basically evolve cards).

As for this deck, it will be played pretty much the same way into every matchup in Aggro and Control respectively (again sorry for the summarized guide I just am short of time but still want to come out with a guide a day). 

Aggro: Control the board with cheap removal, decent minions, and destroy mechs with Earth Shock and Hex. If you go for the version with more removal cards these matchups are easier but once you hit turn 4 and get Thunderhead out, aggro becomes much more doable. Not only that, but after turn 7 when you can get Giggling Inventor if you aren't about to lose the game becomes a lot easier to come back from and once an aggro deck loses control they will probably lose. Also, Zilliax is super nice and gives you a little extra healing and into a deck you know is aggro keeping him is a nice choice.

Control: Into Control, keeping bigger minions and the evolve cards in your hand to help get pressure on the board is very good because if they don't have a response you win and they also give you a lot of time to set up your combos because they aren't apply pressure. Cards like Former Champ work well into these matchups because they apply a lot of early pressure and if you evolve the 1/1 minion into a 6 cost minion it is a lot of surprise pressure out of the blue and if you can bait out removal on it or Giggling Inventor you can be more aggressive later and commit more (eventually playing The Storm Bringer).