Pokémon Emerald Seaglass walkthrough
10 parts, one per checkpoint Pokémon Emerald Seaglass’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: No badges yet
11 areas · 56 trainers · Rival Brendan (Mudkip), Rival Brendan (Torchic), Rival Brendan (Treecko) and 3 more
Part 2: Beat Roxanne — Rustboro City Gym, badge 1
2 areas · 8 trainers · Roxanne
Part 3: Beat Brawly — Dewford Town Gym, badge 2
8 areas · 95 trainers · Winstrate Vivi, Wally, Winstrate Victor and 9 more
Part 4: Beat Wattson — Mauville City Gym, badge 3
11 areas · 73 trainers · Magma Admin Tabitha, Wattson, Magma Leader Maxie and 1 more
Part 5: Beat Flannery — Lavaridge Town Gym, badge 4
1 area · 5 trainers · Flannery
Part 6: Beat Norman — Petalburg City Gym, badge 5
32 areas · 241 trainers · Aqua Admin Shelly, Norman, Rival Brendan (Mudkip) and 7 more
Part 7: Beat Winona — Fortree City Gym, badge 6
1 area · 11 trainers · Winona
Part 8: Beat Tate & Liza — Mossdeep City Gym, badge 7
5 areas · 24 trainers · Aqua Admin Shelly, Tate & Liza, Aqua Leader Archie
Part 9: Beat Juan — Sootopolis City Gym, badge 8
4 areas · 38 trainers · Wally, Juan, Elite Four Sidney and 4 more
Part 10: Beat the Elite Four and the Champion
3 areas · 8 trainers · Brawly (Rematch 1), Roxanne (Rematch 1), Flannery (Rematch 1) and 29 more
It also doesn't say when Altering Cave, Scorched Slab open up, so they are in no part above; each has its own route page.