Walkthrough
Once back at Cinnabar Island after your short Sevii Islands adventure, you will need to head to the eighth and final Pokemon Gym back in Viridian City. The quickest way to get there is by heading north of Cinnabar Island on Route 21. This will take you back to Pallet Town, which is just a short ways away from Viridian City.
Wild Pokemon
Grasses:
Tangela (100%): Levels 17-28
Surfing:
Tentacool (100%): Levels 5-40
Magikarp (100%): Level 5
Horsea(FireRed)/Krabby(LeafGreen) (60%): Levels 5-15
Krabby(FireRed)/Horsea(LeafGreen) (20%): Levels 5-15
Magikarp (20%): Levels 5-15
Horsea(FireRed)/Krabby(LeafGreen) (84%): Levels 15-35
Gyarados (15%): Levels 15-25
Psyduck(FireRed)/Slowpoke(LeafGreen) (1%): Levels 25-35
Pokemon Trainers
Fisherman Wade: Level 27 Magikarp, Level 27 Magikarp, Level 27 Magikarp, Level 27 Magikarp, Level 27 Magikarp, Level 27 Magikarp
Fisherman Ronald: Level 28 Seaking, Level 28 Goldeen, Level 28 Seaking, Level 28 Seaking
Sis & Bro Lil & Ian: Level 33 Seadra, Level 33 Starmie
Swimmer Spencer: Level 33 Seadra, Level 33 Tentacruel
Fisherman Claude: Level 31 Shellder, Level 31 Cloyster
Fisherman Nolan: Level 33 Seaking, Level 33 Goldeen
Swimmer Jack: Level 37 Starmie
Swimmer Roland: Level 32 Poliwhirl, Level 32 Tentacool, Level 32 Seadra
Swimmer Jerome: Level 33 Staryu, Level 33 Wartortle
Pokemon Trainers - VS Seeker Rematch
Fisherman Wade: Level 47 Magikarp, Level 47 Magikarp, Level 47 Magikarp, Level 47 Magikarp, Level 47 Magikarp, Level 47 Magikarp
Sis & Bro Lil & Ian: Level 50 Seadra, Level 50 Starmie
Sis & Bro Lil & Ian: Level 55 Seadra, Level 55 Starmie
Swimmer Jack: Level 50 Starmie