Part 3: Beat Roxie — Virbank City Gym, badge 2

Beat Roxie — Virbank City Gym, badge 2 opens 2 areas.

Where to go

1. Castelia City

   Wild: Audino 90% · Lv 15-18, Cottonee 35% · Lv 15-17, Petilil 35% · Lv 15-17, Rattata 30% · Lv 15-16 +8 more

2. Castelia Sewers

   Wild: Grimer 100% · Lv 5-15, Rattata 45% · Lv 14-17, Zubat 45% · Lv 14-17, Muk 20% · Lv 50-70

Everything you can have caught by this checkpoint · Open the interactive guide

It also doesn't say when 5 of its areas open up, so they are listed together in the last part rather than guessed into the story.