Hearthpwn

Reached legend with this one in the field full of Mech Mages and Pirates (Warriors, also Rogues), so it must be quite good.

Also only 4 cards are from sets other than core or last expansion, so this deck can be valid for a long time.

Murloc Tinyfin - 0 mana makes it really interesting, obviously it's the synergies that make it matter - especially Chum Bucket and Lushwater Scout

Murloc Tidecaller - self-buffing 1 drop, always a staple in any murloc deck

Rock Bottom - much better than it seems, 2 murlocs for 1 mana, like Tinyfin, especially good with Chum Bucket (to buff your hand) and Lushwater Scout (to be buffed)

Sir Finley, Sea Guide - not a 1 drop by any means, unless your starting hand really sucks. You mostly want to play him turn 4 after turn 3 Azsharan Scavenger to get Sunken Scavenger asap

Amalgam of the Deep - best card in set probably, obvious addition for any tribal deck

Chum Bucket - gets you most explosive plays, best followed by Rock Bottom. Don't wait to long for best outcomes, you need to be fast

Lushwater Murcenary - just a solid 2drop, nice follow up after turn 1 Tidecaller, if you don't have more insane plays

Lushwater Scout - this card wins games. Especially if buffed, giving all your murlocs rush and +1 attack is just insane. You can stop other aggro decks from dominating board or get a huge comeback. Coining this against Pirate Warrior is how most winning games against them start. Works great with Rock Bottom

Voidgill - another solid murloc with buff. Good turn 2 play, also after Gorloc Ravager refill

Azsharan Scavenger - Spider Tank for murlocs with upside. With Finley you can play Sunken Scavenger turn 4, but most of the times it will be not as soon or never. Don't hold your dredge cards just to get this.

Coldlight Seer - another staple of murloc decks since forever

Murloc Warleader - same

Twin-fin Fin Twin - best card to buff (especially with Chum Bucket), not too good without buffs though. Great to get back control over board or just put 2 big minions for 3 mana. Rarely turn 3 play, better hold it to make it big most of the times

Bloodscent Vilefin - nice turn 4 play after turn 3 Azshara Scavenger. Also lets you to play Gigafin for life turn 5 which is absolutely ridiculous swing. You can rarely plan it though

Gorloc Ravager - not a cheap card, but draw 3 with body is a great refill. Also good one (if you have spare health) to play from Bloodscent Vilefin

Gigafin - you might not expect murloc based deck to play this one, but it actually fits. Makes great swing especially against decks which eventually win the board against you (Pirate Warrior). Nuts if you can play it of Bloodscent Vilefin. Also, Gigafin has quite low health and your multiple murloc buffs can make him big enough to avoid damage based removal.

How to mulligan - keep Tidecaller, Rockbottom, Chumbucket (only 1), Lushwater Scout, Voidgill are the best cards to keep. You can keep Azsharan Scavenger if you have 2drop too (ideally 1drop as well). Keep any 2drop if you keep 1drop.