Hello There! 

Even tough i think Piranha Swarmer or as i call it Flood Shaman will be pretty bad i still decided to try it out. 

The Gameplan is simple. Flood the board with cheap and many minions and hit face. 

Look for early aggression in the mulligan and also cards like Anchored Totem could get out of hand pretty quick so try to also mulligan for that. Also Peasant is nice for the draw. Keep on flooding the board and finish it off with Bloodlust.

Also if you have the coin you can keep Drek'Thar to keep up the early pressure. 

As i said, i think this type of shaman will not work but maybe im wrong and Flood Shaman will rule them all !!!! 

Good luck and have fun!