Potential movesets
I seperated the Electric-Type Porygon-Z from the Ghost-Type Porygon-Z to avoid confusion with slashes.
Ghost type
Porygon-Z @ Normalium Z
Ability: Adaptability
EVs: 44 Def / 212 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Shadow Ball
- Thunderbolt
- Ice Beam
- Conversion
Electric Type
Porygon-Z @ Normalium Z
Ability: Adaptability
EVs: 44 Def / 212 SpA / 252 Spe
Timid Nature
IVs: 0 Atk
- Thunderbolt
- Ice Beam
- Conversion
- Recover / Shadow Ball / Tri-Attack
44 Defense EVs are used to give Genesect a Special Attack boost instead of an Attack boost, making it more difficult for a Scarf set to revenge kill Porygon-Z. Max Speed is used to outspeed pokemon such as Modest Nihilego, Modest Tapu Lele and Modest Landorus, as well as Scarf Excadrill and Pheromosa after Z-Conversion.
Other spreads to increase the damage output can be used, such as 236 SpA / 228 Spe Timid and 248 SpA / 216 Spe Timid (both with 44 EVs in Defense).
Ghost Type Porygon-Z abuses the fact that many teams lack a Ghost-resist, or have a Ghost-resist weak to one of the coverage moves like Mandibuzz and Greninja. Ghost-Type Porygon-Z is also able to avoid damage from ExtremeSpeed and Mach Punch, making revengekilling more difficult.
Porygon-Z can also transform into an Electric-Type, giving it another strong STAB option and, because BoltBeam has great coverage, the option to use other moves like Recover and Tri-Attack (to be able to revenge kill before using Z-Conversion). It can also get some useful OHKOs Ghost-Type Porygon-Z doesn't achieve, such Toxapex and Tapu Fini (to prevent Haze).