After departing the Aether Paradise, you arrive in the Seafolk Village on Poni Island.
Explore the Village
Go into the floating shop on the left and talk to the guy to get a Magmarizer and Electrizer. Talk to the Ace Trainer in the shop to get Aerodactyl.
Go north and there will be a cut scene.
You can go west into a battle restaurant. There is a green sparkle under the bottom-left table there.
Go east from there and talk to the Rising Star. She asks if you are a lucky person. She will give you an item based on your answer.
To the right, the Veteran says that she will reward you if you catch a regional variant Raichu and show her your Pokédex.
Go south from there, and go to the right to get TM91 Flash Cannon. There is a fishing spot below.
Go back outside and go west to the tree. There is a Veteran named Kumu northeast of the tree who will trade you her Steenee, named Stena, if you trade her a Granbull. Stena comes with Grassium Z. You can find Granbull in the grass to the north.
The Pokémon Center is northwest of that. You can go east from there to find a green sparkle.
Go north and you reach the Poni Wilds.