I just did some calcs. A Wigglytuff with Max HP & Sp.Def with Light Screen up can easily survive a Hyper Beam from Porygon Z.
While it can survive a Hyper Beam from Porygon-Z, I don't think Porygon-Z would be using Hyper Beam, and Wigglytuff having Light Screen is situational at best.
Max SpA Adaptibility Porygon-Z Hyper Beam on Max/Max Wigglytuff with Light Screen - 41.74% - 49.17%
Max SpA Adaptibility Porygon-Z Tri Attack on Max/Max Wigglytuff with Light Screen -
22.31% - 26.45%
It is doubtful that Porygon-Z will even attempt to Hyper Beam Wigglytuff without a NP boost, as Hyper Beam leaves Porygon-Z vulnerable to Status (Sing/Twave) from Wigglytuff, as well as the presence of Light Screen sort of neuters Porygon-Z.
Max SpA Adaptibility Porygon-Z Hyper Beam on Max/Max Wigglytuff
without Light Screen - 82.64% - 97.52%
Max SpA Adaptibility Porygon-Z Tri Attack on Max/Max Wigglytuff
without Light Screen - 44.21% - 52.07%
Without Light Screen, Wigglytuff is raped by Porygon-Z even with Max/Max defenses, and Porygon-Z won't stay in on Wigglytuff to get Twaved/Singed.
These calculations are the same as Porygon-Z with a Nasty Plot boost on Max/Max defenses Wigglytuff with Light Screen.
Max SpA Adaptibility Porygon-Z Hyper Beam
with NP boost on Max/Max Wigglytuff
without Light Screen - 164.88% - 194.21%
Max SpA Adaptibility Porygon-Z Tri Attack
with NP boost on Max/Max Wigglytuff
without Light Screen - 88.02% - 103.72%
Putting Hyper Beam on Specs-Z is not achieving what Hyper Beam was for - OHKOing Blissey with Nasty Plot.
My question is whether a CounterBro would be viable in the metagame. Simply -
Slowbro @ Leftovers
Bold (+Def -Attack)
Own Tempo
252 HP, 212 Defense, 44 Special Attack
Ice Beam
HP Electric/Surf
Counter
Slack Off
Simply for countering Ttar/other physical sweepers that have an SE move on Slowbro, since it gets hit pretty hard by SE moves and CBChomp EQ does ~50% to it.
Ice Beam is for ScarfChomp/DDMence, Surf could go over it.
HP Electric is for Gyarados.