Pokemon GO's Arlo lineup in August 2020 can cause trouble if you're not careful which is exactly what you would expect from a member of Team Rocket. Pokemon GO Fest is over, so players are back to working on specific Research tasks they may still have and that includes "Rocket Straight to Victory."
On Day 2, players are requested to defeat leaders of Team Rocket including Arlo. However, his lineup hasn't changed from his usual group of Pokemon. It's different from the Go Fest, but not his standard set up.
He'll start with a Pineco, then either use a Blastoise, Charizard, or Steelix. When you defeat the second one, he'll use a Dragonite, Salamence, or Scizor.
Pokemon GO Arlo August 2020: How to Defeat Arlo's New Lineup
Pineco is a Bug-type Pokemon that can utilize Bug, Ground, Normal, Rock, and Steel attacks. Go after it with a fire type and you'll be solid.
Blastoise and Charizard are fairly self-explanatory, and you should attack them with an Electric and Rock-type Pokemon respectively. Steelix is also a straight forward fight and needs a strong Fire-type Pokemon to fight it.
As for the third Pokemon, Dragon Pokemon can be tough.
Dragonite and Salamence both struggle against a strong Ice-type Pokemon, and bring the same Fire-type Pokemon from the Steelix fight and you'll decimate the Scizor.