Pokémon Platinum walkthrough
11 parts, one per checkpoint Pokémon Platinum’s own documentation defines: the areas each one opens, the wild Pokémon and trainers in them, and the fight at the end of it. Everything here is read off the game’s own files, so anything it doesn’t state isn’t claimed.
Part 1: Just started — no badges
15 areas · 77 trainers · Commander Saturn, Team Galactic Boss Cyrus, Commander Mars and 14 more
Part 2: Beat Roark — Oreburgh City Gym, badge 1
8 areas · 34 trainers · Commander Mars, Roark
Part 3: Beat Gardenia — Eterna City Gym, badge 2
8 areas · 43 trainers · Commander Jupiter, Gardenia
Part 4: Beat Fantina — Hearthome City Gym, badge 3
7 areas · 54 trainers · Rival Barry (Chimchar), Rival Barry (Piplup), Rival Barry (Turtwig) and 1 more
Part 5: Beat Maylene — Veilstone City Gym, badge 4
7 areas · 27 trainers · Rival Barry (Chimchar), Rival Barry (Piplup), Rival Barry (Turtwig) and 1 more
Part 6: Beat Crasher Wake — Pastoria City Gym, badge 5
11 areas · 81 trainers · Rival Barry (Chimchar), Rival Barry (Piplup), Rival Barry (Turtwig) and 2 more
Part 7: Beat Byron — Canalave City Gym, badge 6
8 areas · 36 trainers · Byron
Part 8: Beat Candice — Snowpoint City Gym, badge 7
6 areas · 22 trainers · Team Galactic Boss Cyrus, Candice
Part 9: Beat Volkner — Sunyshore City Gym, badge 8
6 areas · 58 trainers · Champion Cynthia, Champion Cynthia — rematch, Elite Four Aaron and 11 more
Part 10: Beat the Elite Four and the Champion
11 areas · 60 trainers · Commander Jupiter, Commander Mars, Rival Barry (Chimchar) and 2 more
Part 11: areas the documentation doesn’t place
4 areas
This game's documentation doesn't say where 21 of its 513 fights happen, so those trainers are on no part of this walkthrough; they are all on the Trainers page. It also doesn't say when 4 of its areas open up, so they are listed together in the last part rather than guessed into the story.