Curse is P2's traditional GSC set, but my opinion is that it's really just an extra, lesser Snorlax if you use it that way (read: totally redundant). It does beat Lax in a Curse war, though, so it has that going for it. The set I use, though, foregoes Curse for Thunder Wave (and Double-Edge over Return as the STAB, it hits most things surprisingly hard). With Double-Edge, Ice Beam, Twave, and Recover, P2 functions kinda like a mixed wall, mixed attacker, and support mon all in one. Double-Edge is a possible 3HKO on Raikou and possible 4HKO on Snorlax, and Ice Beam 3HKOs Zapdos without recoil. Without those key mons switching in all day, Porygon2 spreads status way more reliably than other status-centric mons. Its general tankiness and access to Recover means it can safely tank common threats on offensive teams such as Steelix, Gengar, and Exeggutor, so it gets a bunch of opportunities to come in and cripple the opposing team. Not a whole lot outright forces it out, either, making it almost Zapdos-esque in its ability to just stay in on shit. That said, all these switch-in opportunities can always just... explode on Porygon2, especially as its ability to threaten most of its switch-in targets is limited (e.g., neutral Ice Beam on Steelix and Gengar is no more than a 4HKO). Thus, more often than not, it ends up going 1-for-1. That's okay, though, because P2 is not a specific wall for anything, just a general tank, so you're wasting one of their wallbreakers by baiting them into Exploding on P2. Porygon2 doesn't match up as well against more defensive teams, where Spikers, Suicune, and Miltank are more likely to be present to set up on, neutralize, and undo paralysis spread by Porygon2, respectively. However, P2 still functions well against defensive teams, as Recover ensures it isn't trivial to just wear it down through attrition, it still gets plenty of opportunities to switch in, Twave can still make life awkward for Suicune and Spikers, Miltank will run out of Heal Bells eventually, and if all else fails, P2 can go for the freeze with Ice Beam. Porygon2's biggest problem, though, is its weakness to status. It doesn't want to be paralyzed and possibly not get that key Recover off, and it doesn't want to take a Toxic and be forced into Recover loops all day. It's kinda slow and juuuust tanky enough to deal with most things, so status really screws with how effective it can be. What's more, you probably aren't adding a Heal Beller on top of a P2 team, as you already have two Normal-types on your team (P2 and the mandatory Snorlax). In fact, I think I lied, the real worst thing about Porygon2 is that its typing makes it difficult to squeeze on a team without feeling like you're skimping on defensive synergy.