For a list of the move changes see https://gamepress.gg/pokemongo/go-battle-league-season-3. Below I’ll muse on potential impact on PvP.
Drill Peck deals more damage - Shadow Zapdos is now even more threatening and that’s really the only Pokemon affected. The list of Drill Peck users is short - Natu, Piplup, Spearow, Doduo, Dodrio, Murkrow, and Zapdos.
Brave Bird deals more damage and severely lowers the user’s Defense (3 stages) - This better hit like a truck because that it a heavy debuff.
Infestation generates energy faster - A good change for Pokemon like Garbodor which relies on Gunk Shot. It can now spam Body Slam even more which pressures shields and opens up the potential to land a Gunk Shot. While I have not ever used Swalot, I hear good things and this change will make it even better.
Hex generates energy faster - Hex is an Infestation clone already so likely to remain that way. A nice boost for Drifblim and Frosslass and Jellicent once it’s released. For those with access to Hex and Shadow Claw we’ll have to see how they stack up.
Powder Snow deals more damage - Froslass making out again plus Mamoswine and Alolan Sandslash. The underrated Sealeo gets even better.
Blizzard deals more damage - Did I mention Sealeo? Froslass making out like a bandit again. I don’t need to tell you about Whiscash.
Flash Cannon requires more energy - Skarmory never used FC anyway but this is a hit to Registeel. Ferrothorn has other good charge move options and Bastiodon tends to favor Stone Edge and Flamethrower. Empoleon takes a hit but with the damage boost to Blizzard the increased energy may be worth it.
Focus Blast deals less damage - A hit to many Pokemon notably the Regis and Mewtwo. Sorry to those who just put FB on their Community Day Gengars.
Moonblast has a lowered chance of lowering enemy attack - Cresselia was attacked viciously and publicly.