if...

Neither, they fuse into Porytom xD

 

Power to the Porytom.
I think it would boot the Porygon out, personally. Then they'd get into a fight over appliances.

 

Porygon can travel through cyberspace, but Rotom only travels through electrical devices. They wouldn't really meet, unless Rotom enters the device hosting the network that the Porygon is inside.

My question is why Porygon isn't a ghost-normal type. While not a spirit or anything it has the same physical properties of a ghost. It's made of computer programming which isn't a solid last time I checked, and it can enter certain objects. I think it would have been a cool typing.

 

it would indeed by a cool typing and make more sense if Porygon had been ghost type too, but I doubt that ever happen.
most likely the Porygon would be forced out or Rotom would find it unable to posses the object. that or we will get a Jogres Evolution, which also means we have jumped to another franchise.

 

Holy shit, the advantages a Normal/Ghost type would have lol. Bye bye, Fighting Weakness. And it would be immune to Ghost type moves while being able to dish them out, and also be immune to normal type moves. Damn, so many immunities , give it levitate and you've got another (unless the opponent has mold breaker) xD. Dark-type would really be the only problem for that type imo.

 

They would just both be there. As a ghost type, Rotom cant touch the normal type Porygon, and vice versa. They would both just be chilling there '3'