Niantic has been known to make alterations to certain moves as Pokémon GO seasons of GO Battle League change. Now, as Season Three ends and Season Four begins, Niantic has rolled out new moves that will affect how select Pokémon perform in PVP in general, which impacts friend battles, GO Battle League, and Team GO Rocket battles. Raiders take note as well because while these changes don't impact raids, Niantic has also announced a new move that can be added to a certain Pokémon's moveset that can be used in any battles.
In their announcement for GO Battle League Season Four, Niantic wrote of these upcoming changes:
Lunge: This Bug-type Charged Attack will lower the opposing Pokémon's Attack. Initially when this attack becomes available, only Masquerain and Galvantula will be able to learn it.
The following attacks have been updated for Trainer Battles:
Bug Buzz: This Bug-type Charged Attack now has a chance of lowering the opposing Pokémon's Defense.
Flame Charge: This Fire-type Charged Attack now deals less damage and will raise the user's Attack.
Signal Beam: This Bug-type Charged Attack now has a chance of lowering the opposing Pokémon's Attack and Defense.
Along with these updates to existing attacks, the following Pokémon can learn an attack it couldn't before. Vespiquen and Signal Beam: This powerful Bug-type attack is a perfect fit for a powerful Bug-type Pokémon like Vespiquen.
While most of these changes only impact PVPers, as the lowering of attack/defense doesn't work in raids, Vespiquen learning Signal Beam is indeed something that trainers can take with them into any battle, not just in bouts with other trainers. Most of these moves will enrich Bug-type Pokémon, which is of note due to the prominence of Mega Beedrill in Pokémon GO's September events. In addition to these new moves, all Bug-types will be boosted when any trainer brings a Mega Beedrill into a raid battle.