Poisonous is a very powerful effect that can turn even the smallest minions into real threats. On top of that, Murlocs have received serious attention in this meta. From the looks of it, Murloc decks are returning with a blast.
Toxfin will definitely see play in all of those decks, as it is neutral and incredibly cheap.
For most, the best choice for it would most likely be Murloc Shaman, as it has got some amazing Murlocs in the Rise of Shadows expansion.