Just an easy (budget!) deck if you're struggling against the Fish Boss.
Basically, hard mulligan for Wild Pyromancer (THE most important card!), and pray to draw Zombie Chow and Deathlord early game too. With this set up, most people beat it on their first or second try.
If these conditions are met, you should be able to clear the murlocs every turn with Pyro and spells from turn 4 until the end of the game. Don't try to rush and be very careful about your master burner's Health. The combo Northshire Cleric + Circle of Healing is also key to be able to draw the required number of spells not to run out of gas to burn.
Your mileage may vary, but here is an example of what the final turn may look like :