Walkthrough: At the end of Route 11 is none other than Route 12. Route 12 is a rough Mountainside that requires a Mudsdale in order traverse the rocky terrain, which is why Hapu, the trainer you helped defeat Team Skull at Royal Avenue with, shows up and gives you access to the Mudsdale Poke Ride. Route 12 connects to Route 13, with access to both Blush Mountain and Secluded Shore.
Wild Pokemon:
Grasses (Levels 25-29): Geodude(40%), Mudbray(30%), Torkoal(20%), Elekid(10%)
SOS Pokemon #1 (Levels 25-29): Geodude, Mudbray, Torkoal, Electabuzz
SOS Pokemon #2 (Levels 25-29): Geodude, Mudbray, Torkoal, Chansey
SOS Pokemon #3 (Levels 25-29): Geodude, Mudbray, Torkoal, Elekid
Zygarde Cells: There are two Zygarde Cells found here.
Trainers:
Punk Guy Lane - Level 29 Krokorok
Punk Girl Yoko - Level 29 Panchem
Rising Star Leilani -Level 30 Tirtouga
Rising Star Matthew - Level 30 Cranidos
Scientist Jayson - Level 28 Porygon, Level 29 Magneton
Collector Andrew - Level 28 Ledian, Level 29 Pinsir
Items:
Burn Heal - First Jagged Terrain
Elixir - Near Rising Star Leilani
Hyper Potion - Grass Near Rising Star Matthew
X Attack - Grass Southeast Route
PP Up - In Southernmost Rock (Hidden)
TM77 Psych Up - Defeat Collector Andrew