What Goldenknight said is practically essential to the usage of Porygon. If you're going to use Porygon, read his post!
Originally Posted by Fat Methmite
Porygon really suffers from the fact that its normal type. fightings tend to roll the fuck all over it.
Mienfoo, timburr, hell even Scarf-chop can just beat it to hell and back before it has the opprotunity to do much else that get its Download boost. running larvest like ray said is a good way to deal with it; but its important to remember to deal with it at all when you decide to run him.
Porygon is not a standalone Pokemon in the way Mienfoo or Chinchou is. Although it doesn't need an entire team to support it, it definitely means that you need to run good Fighting-type counters like Eviolite Gastly or Larvesta. Remember that against most teams you will not be sweeping with Porygon until late-game—unless it's a heavy stall team and you manage to dodge Toxic. Porygon is a situational counter, and by that I mean for the early- to mid-game you should not be taking too much damage and Recovering instead of going for kills (like Goldenknight said).
Originally Posted by Fat Pen Ink
I can say that Porygon is a really good Trick Room abuser (albeit, waaay better in 4th Gen. In fact, I don't even think he can be used with TR in 5th Gen). I used Trick Room throughout half of 4th Gen (after Missy, which I wasn't there for), and he was fucking incredible. I believe I ran something like:
Porygon @ Life Orb
EV's: Max Sp.A, etc
- Tri Attack
- Trick Room
LO STAB Tri Attack hit like a fucking truck. Seriously, I could suicide lead my TR Exeggcute and go out right to Porygon and start sweeping. Unfortunately, Porygon really can't run a raw power set anymore, even in TR. Eviolite makes shit way too hard to KO along with so much fighting types it's not funny (and, no surprise there, they all run Eviolite).
This is a powerful set, but in the current metagame you can't OHKO Mienfoo via Tri Attack, which forces you into using Psychic for one of your coverage moves (pretty bad move outside of hitting Mienfoo) so the overall viability of offensive TR Porygon is limited. As a Trick Room supporter however, it is one of the best due to the combination of bulk and Recover. It also synergizes pretty well with Slowpoke, as Slowpoke can Trick Room on Mienfoo, Croagunk, and Timburr while Porygon easily gets a Trick Room up on Chinchou and Staryu.