Route 23

Walkthrough
After obtaining all eight Pokemon Gym Badges and defeating your Rival once again on Route 22, you will be able to proceed past the Gym Badge Checkpoints towards Route 23. This is a very long path full of Wild Pokemon, one that will lead you towards Indigo Plateau (where the Pokemon League is found). Victory Road, a cave full of some of the toughest Pokemon Trainers in the Kanto Region, is also found within the middle of Route 23.

Wild Pokemon
Grasses:
Mankey (30%): Levels 32-34
Fearow (25%): Levels 40-44
Ekans(FireRed)/Sandshrew(LeafGreen) (20%): Levels 32-34
Spearow (15%): Levels 32-34
Arbok(FireRed)/Sandslash(LeafGreen) (5%): Level 44
Primeape (5%): Level 42

Surfing:
Psyduck(FireRed)/Slowpoke(LeafGreen) (100%): Levels 20-40

Old Rod:
Magikarp (100%): Level 5

Good Rod:
Poliwag (60%): Levels 5-15
Goldeen (20%): Levels 5-15
Magikarp (20%): Levels 5-15

Super Rod:
Poliwag (40%): Levels 15-25
Poliwhirl (40%): Levels 20-30
Gyarados (15%): Levels 15-25
Psyduck(FireRed)/Slowpoke(LeafGreen) (5%): Levels 15-35

Items
Leppa Berry: ItemFinder
Max Ether: ItemFinder
Ultra Ball: ItemFinder
Aspear Berry: ItemFinder
Full Restore: ItemFinder
Sitrus Berry: ItemFinder
Lum Berry: ItemFinder
Max Elixir: ItemFinder