Surfing Detour

From Santalune Forest, head west on Route 3 and Surf across the water to find a Dawn Stone. This stone evolves male Kirlia into Gallade and female Snorunt into Froslass.

If you haven't used Cut yet, go north along the ground of Route 3 to find a Cut tree. Beyond it, you'll find a Revive.

From Ambrette Town, head north on Route 8 to the Mago Berry tree.

Surf northwest from the Mago Berry tree. You may need to stand northwest of the tree to encounter a Sky Trainer from an island.

North-northwest of the Sky Trainer's island, you'll find a sandy island. Examine a rock there to find a Heart Scale.

North of the sandy island, Surf and battle a Swimmer.

On the nearby island, you can find TM19, which teaches Roost. Roost is a move for Flying Pokémon that makes them land, briefly lose their Flying-type, and recover HP.

Another Swimmer is patrolling the rock formation to the southeast. Battle them.

North of the rock formation, within Cyllage City borders, you'll find a house on an island with a TV. The child inside will give you a Charti Berry, which weakens super-effective Rock-type moves.