Does anyone have any good advice for a half-pirana deck?
What's your other half? A low star half-deck is Tula Tyd Hawkins Ulrich (10*s only) Piranas are good in that you can basically mix and match them:
2*s - Hawkins, Tula, Hawkins Noel
3*s - Tyd, Urich, Ector, Andsom
4*s - Kristin, Raeth
5*s - Selma, Bloodh
Mix and match any number of those and you have a decent half deck.