Walkthrough
Just south of Water Path is Ruin Valley, an enormous area full of Wild Pokemon and Pokemon Trainers. Also located within Ruin Valley is the Dotted Hole, a cave that can only be explored by using HM Cut on the door.
Wild Pokemon
Grasses:
Natu (25%): Levels 15-20
Spearow (20%): Level 44
Fearow (15%): Level 49
Meowth (10%): Level 43
Yanma (10%): Level 18
Wooper(FireRed)/Marill(LeafGreen) (10%): Level 15
Persian (5%): Levels 49-52
Psyduck(FireRed)/Slowpoke(LeafGreen) (5%): Level 41
Wobbuffet (5%): Level 25
Surfing:
Wooper(FireRed)/Marill(LeafGreen) (100%): Levels 5-25
Magikarp (100%): Level 5
Poliwag (60%): Levels 5-15
Goldeen (20%): Levels 5-15
Magikarp (20%): Levels 5-15
Poliwag (40%): Levels 15-25
Poliwhirl (40%): Levels 20-30
Gyarados (15%): Levels 15-25
Psyduck(FireRed)/Slowpoke(LeafGreen) (5%): Levels 15-35
Pokemon Trainers
Hiker Daryl: Level 50 Sudowoodo
PokeManiac Hector: Level 49 Rhyhorn, Level 49 Kangaskhan
Ruin Maniac Stanly: Level 48 Graveler, Level 48 Onix, Level 48 Graveler
Ruin Maniac Foster: Level 50 Golem
Ruin Maniac Larry: Level 49 Machoke, Level 49 Machoke
Pokemon Trainers - VS Seeker Rematch
PokeManiac Hector: Level 55 Rhydon, Level 55 Kangaskhan
Ruin Maniac Larry: Level 54 Machoke, Level 54 Machoke
Items
Sun Stone: On Ground
HP Up: On Ground
Full Restore: On Ground