Porygon2 already had a POTW:
www.serebii.net
Porygon-Z, the Evolution to Porygon2 has the troubled history you would expect of an illegal upgrade, whose main benefit is that Porygon2 (the official upgrade) can use Eviolite. Porygon-Z has some obscene highs: its Nasty-Plot Adaptability Hyper Beams can cleave through even Blissey without issue and its Z-Conversion set was incredibly threatening, but each high comes with a catch. Base 90 Speed is fast, but still leaves it outsped by much of the competition. Base 135 Special Attack is great, but misses the mark without boosting. Porygon-Z's movepool is great, but lacks moves to answer Steel types. Oh right, Z-Conversion is no longer a thing and Porygon-Z struggles to abuse Dynamax the same way. Porygon-Z really needs a way to bolster both its Speed and Special Attack simultaneously... And/Or Flamethrower.
Trojan Patch.exe
Porygon-Z
Ability: Download
Item: Focus Sash/Chople Berry
-Agility
-Nasty Plot
-Ice Beam
-Thunderbolt
Nature: Modest (+SATK, -ATK) or Timid (+SPE, -ATK)
EVs: 4 HP / 252 SATK / 252 SPE
Double Dance Porygon-Z. Use Agility or Nasty Plot depending on the situation -Agility when going up against faster frailer teams, and Nasty Plot when going up against defensive tanky teams. BoltBeam is chosen for best range of Neutral+Super Effective coverage. Dynamax doesn't do much for this set as Porygon-Z can't boost while D-Maxed. EVs and Nature are to maximize damage. Item is to ensure Porygon-Z lives to boost, as it is rather frail and lacking in resistances. Since we aren't using any normal STAB, Download is the ability of choice, as the possibility of nabbing a Special Attack boost off of Download can turn Porygon-Z into a monster after Agility (Analytics doesn't work as we don't want to take a hit or go 2nd and will use a predicted Switch to setup).
This set needs team support to work at its best as Porygon-Z struggles to find moments to setup. Dual Screens, Sleep are the recommended methods of doing so.