it is a utility counter which checks gyarados and dragonite with boltbeam coverage and it traces plenty of great abilities from otehr pokesmon such as levitate from flygon and flash fire from heatran, it can also trace intimidate to help vs gyarados. it can eventually trap magnezone and force a twave on it with teampartner such as brick break scizor which can beat parad magnezone. that is pretty much about it.
it can also be a trick room setter for teams with the traits of switching into pokemon like heatran and gengar, to set trick room on them with its okay defensive stats. porygon2 supports teammates such as bronzong, heatran, machamp and other pokemon, for abusing trick room. but trick room isnt its main niche in dpp ou.
is a very niche curse-sweeper with having recovery and it can check water-types such as swampert and suicune due to its great typing.
on the other hand can act under trick room, due to its natural low speed its an effective trick room-abuser. furthermore it has great special attack to profit from under trick room with its stab-options in fire blast and earth power, which makes it difficult to switch into. furthermore it can run hidden power ice to nail latias and moreover flygon.