This deck is incredible. I just got legend for my first time ever with this, and it was honestly pretty easy. Credits for this deck goes to /u/FU4FREE on reddit. Your primary focus is to flood and control the board until you have a lethal setup (with warleader or bloodlust). This meta doesn't have many board clears compared to most so you can go very wide usually.
Keep the following cards in mulligan:
Muloc Tidecaller, Murmy, Underbelly Angler, Mogu Fleshshaper, Sludge Slurper
Use Mutate on Mogu Fleshshaper whenever possible (you'll get about a 6.5/6.5 on average from my limited experience). The next best targets (if you are desperate) are probably Coldlight Seer and Murloc Tidehunter
Some basic matchup tips:
Quest Druid/Shaman/Rogue: Just go all in and you usually win by the time they finish their quest. They don't play board clears so not much risk
Control Warrior: Just hope they don't have board clears. This is probably the worst matchup. You'll usually lose
Highlander Hunter: Just control the board and set up lethal. Be prepared for them to play Zephrys for Hungry Crab. Play around secrets if possible, but don't be too scared of explosive trap. They only have 1 copy.
Murloc Paladin: Just go as wide as possible. When they play Tip the Scales on turn 5 (which is almost every game), either push for lethal or trade their board away so they only have 2-3 murlocs and you have 6-7. From there, you'll usually win
Rush Warrior/Zoolock/Priest/Aggro Rogue: Just flood and control the board (with value trades) until you have lethal (with bloodlust or warleader.