Most of these Routes have a 100% Encounter rate (or add up to 100%) for their chosen Pokemon and the respective stat:
HP - Rusturf Tunnel (Whismur)
Level: 5
1 HP each 5 = 5 HP
Attack - Mt. Pyre (Shuppet)
Level: 15
1 Atk each 5 = 5 Atk
Defense - Route 111 (Sandshrew)
Level: 11
1 Def each 5 = 5 Def
Special Attack - Route 119 (Oddish) or Route 113 (Spinda)
Level: 13 (Oddish), 9 (Spinda)
1 SpA each 5 = 5 SpA
Special Defense - Route 115 (Swablu)
Level: 10
1 SpD each 5 = 5 SpD
Speed - Route 104 (Zigzagoon, Wingull or Taillow)
Level: 2
1 Spe each 5 = 5 Spe
Notes:
Sweet Scent/Honey actually work in overworld Sandstorm/Rain unlike in previous games
Shuppet Appears in the Cemetery Area of Mt Pyre
Petaburg Woods divides Route 104 in two. (North – Wingull, South – Taillow)
Pokérus will double the EVs gained, and stacks with the items below:
Macho Brace (Doubles total EVs gained) - Route 111
Power Items - Battle Resort
Anklet (+4 Speed per Pokemon defeated)
Band (+4 Sp. Def per Pokemon defeated)
Belt (+4 Defense per Pokemon defeated)
Bracer (+4 Attack per Pokemon defeated)
Lens (+4 Sp. Attack per Pokemon defeated)
Weight (+4 HP per Pokemon defeated)
Source
