As with all games, as you complete your Pokédex, you will receive a variety of gifts to celebrate it. While previous games have adopted the idea of merely seeing the Pokémon in your Pokédex to complete it, Pokémon Sun & Moon have returned to the classic concept of having to capture the Pokémon in order to properly register it.

10 Pokémon - Ultra Balls

Location: Hau'oli City

In the Hau'oli City Information Center, a scientist would like to speak to you when you have captured 10 species of Pokémon. When you return with that having been done, he will give you Ultra Balls.

50 Pokémon - Lucky Egg

Location: Route 1

After you have defeated the Elite Four, when you have registered 50 Pokémon in your Pokédex, Professor Kukui will move to the back of his laboratory. If you speak to him, he will give you a Lucky Egg.

300 Pokémon - Shiny Charm

Location: Heahea City - Game Freak HQ

When you have registered all 300 Pokémon in your Alola Pokédex (not including Magearna or Marshadow), you can go to speak to the Game Director in Heahea City's GAME FREAK headquarters. He will congratulate you on completing the dex, give you a stamp for your Trainer Passport and give you the Shiny Charm.