Porygon needs a decent STAB O.o
Well I used this set:
Porygon-Z@Salac Berry
Trait: Adaptability
Moves:
Ice Beam
Thunder
Tri Attack
Endure
Porygon-Z@Focus Sash
Trait: Adaptability
EV: 252 Sp Atk/200 Spd/52 HP
Ice Beam
-Thunderbolt
-Tri Attack
-Agility
It's always a option.
Ah Porygon-Z can learn Agility... Gee never realised that xD
The only thing this set has problems with is
a) Blissey wall (but then again, Porygon-Z ALWAYS hated Blissey
b) Stealth Rock/Spikes trap
this set is awesome if you have a Rapid Spin support