Upgrade:
Flavor: Porygon2 - "Sometimes, it may exhibit motions that were not programmed", "It may have unprogrammed reactions."
Competitive: This creates new ways of doing shenanigans with Porygon-Z. Nasty Plot activates Dark Pulse, Thunder Wave activates Thunder(/bolt), Recover activates Tri Attack or Hyper Beam, Agility activates Psychic or Psyshock, etc.
I think you basically said "everytime Porygon-Z (or any Porygon) uses a status move, it uses a random attacking move of its type that it can learn with x0.5 power."
So basically if Porygon-Z used:
Thunder Wave or Magnet Rise, it will use Thunder, Thunderbolt, Charge Beam, Discharge, Electroweb, Shock Wave or Hidden Power Electric
Agility (or any Psychic type status), it will use Dream Eater, Psybeam, Psychic, Psyshock, Zen Headbutt or HP Psychic
Recover (or any Normal type status), it will use Double-Edge, Facade, Frustration, Giga Impact, Hyper Beam, Last Resort, Return, Round, Secret Power, Snore, Tri Attack or Uproar.
Nasty Plot or Embargo, it will use Dark Pulse, Foul Play, Thief or HP Dark
Sunny Day, it will use HP Fire
Rain Dance, it will use HP Water
Toxic, it will use HP Poison
Nightmare, it will use Shadow Ball or HP Ghost.