Walkthrough: Connected to Poni Plains is the Poni Coast, which connects Poni Plains to Poni Gauntlet. It's a pretty empty area, outside of a given trainer her and there.
Wild Pokemon:
Initial Pokemon - Dustpiles (Levels 56-59): Dugtrio(100%)
Trainers:
Sightseer Noriko - Level 58 Ninetales, Level 59 Exeggutor
Sightseer Devin - Level 58 Sandslash, Level 59 Golem
Zygarde Cells: There is two Zygarde Cells found in Poni Coast.
Items:
Comet Shard - North of Sightseers
Max Revive - Near Sightseers
TM97 (Dark Pulse) - Southern Part of Area