Trace is an incredible ability that allows Porygon to check a huge amount of major threats. Combine that with Porygon's beast defenses (it can tank Brave Birds all day) and you have the greatest utility counter in all of LC. But we already know that. What most people don't focus on is Porygon's stellar Special Attack. It is as high as Missy's, but Porygon has STAB and coverage moves with higher BP than Missy, which allows it to run pretty good offensive sets. With Agility and LO Porygon can serve as a solid late-game cleaner, and with a Scarf it becomes the second best Double Rush counter in the game thanks to Trace, and can also Trick it's Scarf onto Lileep or Hippopotas after it has taken care of Drilbur/Sandshrew. Porygon is a very, very versatile Pokemon that is unfortunately viewed as a one-trick pony by a lot of players, so I'm really glad it was chosen for this PotW.
Twas bryllyg, and ye slythy toves
Did gyre and gymble in ye wabe:
All mimsy were ye borogoves;
And ye mome raths outgrabe.