Looks nice but do i need someone with poison and if i do which one is better Greesh or Pesth?
You don't need a poison in a Piranas deck. Pesth is better, but not good enough to build a deck around. Unless you're on a budget, then he's awesome.
Out of the two, I'd say Greesh. But if you want to inflict a lot of poison damage, I'd advise you to play Freaks instead. Alternatively, you could make a deck with powerful poisoners like Dolly, Muze, Greem or Karrion.