Walkthrough
Berry Forest is the final area within Three Island, being found directly after Bond Bridge. At the very end of Berry Forest, you will find Lostelle, However, she is being held captive by the Wild Pokemon known as Hypno. After defeating the Hypno, you and Lostelle will return to the Two Island Game Corner. Once you do, you will be able to give the Meteorite to Celio's Friend. After this has been completed, you can return to Bill and Celio on One Island in order to return to Cinnabar Island so you can continue your Gym Challenge.
Wild Pokemon
Grasses:
Pidgeotto (20%): Level 37
Gloom(FireRed)/Weepinbell(LeafGreen) (20%): Level 35
Pidgey (10%): Level 32
Oddish(FireRed)/Bellsprout(LeafGreen) (10%): Level 30
Venonat (10%): Level 34
Drowzee (10%): Level 34
Venomoth (5%): Levels 37-40
Psyduck(FireRed)/Slowpoke(LeafGreen) (5%): Level 31
Hypno (5%): Levels 37-40
Exeggcute (5%): Level 35
Surfing:
Psyduck(FireRed)/Slowpoke(LeafGreen) (95%): Levels 5-40
Golduck(FireRed)/Slowbro(LeafGreen) (5%): Levels 35-40
Magikarp (100%): Level 5
Goldeen (60%): Levels 5-15
Poliwag (20%): Levels 5-15
Magikarp (20%): Levels 5-15
Goldeen (40%): Levels 15-25
Seaking (40%): Levels 20-30
Gyarados (15%): Levels 15-25
Psyduck(FireRed)/Slowpoke(LeafGreen) (5%): Levels 15-35
Lostelle:
Hypno: Level 30
Items
Full Heal: On Ground
Max Ether: On Ground
Max Elixir: On Ground
Iapapa Berry: ItemFinder
Cheri Berry: ItemFinder
Wepear Berry: ItemFinder
Oran Berry: ItemFinder
Persim Berry: ItemFinder
Pinap Berry: ItemFinder
Aspear Berry: ItemFinder
Bluk Berry: ItemFinder