Hearthpwn

Tried everything, threw against him everything I had and even more. Died like 15 times. I was very, very angry.

Killed him at first attempt when I tried to use a full-face Murloc deck out of despair. Just let him basically commit suicide while you try to keep board control. Emphasis on removing his Tidecallers asap.

Attached, deck I used. Cheers

I was able to take him down on my first try with a Tempo/Freeze Mage deck. I also got lucky, as he didn't have turn one Tidecaller.

 I used this:

Let his murlock boardflooding work at your favor!

Nah trust me I thought so at first. I mean I packed all kinds of AoE thinking how easy it would be. "Just clear the board and you win" - I said.
But no. He has 50 CARDS, meaning you clear his board, and then he just immediately begun refilling it.

So the key is. How can I use AoE AND get a way to kill him? The answer is: Summoning Stone. With this, your Blizzard doesn't only clear the board and freeze surviving minions, it does also summon a 6 mana minion for you! And then you proceed with a Flamestrike, get a 7 mana minion and so on.

Thats how I beat it :)

I beaten him with Summoner Stone spell based priest.

As long as you get wild pyro in your starting hand and keep it alive you basically won.

If i would be you i would add Murloc Tidecaller to deck you will use i manged to steal it with thoughtsteal and that card accelerated my win.

Patron= easy win once the engine is going you won he doesn't have aoe.. Use Warrior of course. 

Won on first attempt but then it took me a while to win again 4-5 games so you need a little luck.

http://www.hearthpwn.com/decks/395745-heroic-giantfin-guaranteed-kill-first-try-animated

If you're having troubles with Heroic Giantfin, just wrote up a short guide for an almost guaranteed kill first try.  Hope this helps!

I beat him pretty easily on Heroic with Dreadsteed Warlock

I went a completely different route from everyone else it seems!

he doesn't seem to like killing his own murloca except for certain minions. So I played priest, silenced any of his bad ass murlocs and then healed like mad to keep myself alive (tournament medic, flash heals, lightwell, power word glory)

i ended in a loop where after tournament medic and lightwell alone he was only doing 2 damage a turn net, (flash heals and antique healbots allowing me to go the distance) I then kept plugging away until I drew divine spirit and inner fire for my tournament medic - and that was that.

he will leave the lightwell alone and go for face, same with the medic, although northshire cleric he will kill

I beat him on my second try with a Warlock deck playing all the board clears and some Mistress of Pain combos to regain life. Pretty wonky, but good enough, I guess.

Beat it with tempo mage.

In the end I'm going back with "yes" it may be possible for others, but clearly it's impossible for me. Several decks, dozens of attempts and nothing.

That thing is pure incoherent evil.

Quote from Astrohawke18 >>

Guaranteed easy win Heroic Giantfin Patron Warrior Unknown Deck by Astrohawke18 - Dec 3, 2015 View Deck String Export to BBCode Export to Cockatrice Export to MarkDown Export to Html Clone this deck
Minion (18) 2x Armorsmith 2x Frothing Berserker 2x Grim Patron 2x Wild Pyromancer 2x Acolyte of Pain 2x Cruel Taskmaster 2x Explosive Sheep 2x Mad Bomber 2x Unstable Ghoul	Ability (8) 2x Revenge 2x Inner Rage 2x Slam 2x Whirlwind	Weapon (4) 2x Death's Bite 2x Fiery War Axe
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Try my patron deck. Probably one of the easiest heroic wins. Much more consistent than the freeze mage decks imo.

 http://www.hearthpwn.com/decks/385323-guaranteed-easy-win-heroic-giantfin-patron-warrior

That is the highest rated deck on tthis site and I did it first try with it.