Over the last few weeks, different versions of Ash's Pikachu have been available in Pokémon Sun and Moon wearing hats with various emblems on them. For example, the first wave of Pikachus were wearing Ash's famous cap. Now, Pikachu is wearing a cap with the Unova Pokémon League logo on it—and it's now available to download for free.
You can get Ash's Pikachu wearing the Unova Cap right now by using the code PIKACHU20 via the Mystery Gift option at the main menu in Pokémon Sun and Moon. You can pick up your new Pikachu at any Pokémon Center throughout the game by speaking to the delivery person that appears after you redeem your code.
Keep in mind that you can only redeem a code and receive one of the six Ash's Pikachu variations. So if you already picked up one with Ash's classic hat or another Pikachu before, you won't get to add another to your collection.
Your Unova Cap Pikachu will come with the Pikashunium Z Z-Crystal, which powers up the already threatening Thunderbolt move into the Z-Move "10,000,000 Volt Thunderbolt." It sounds a little excessive, but anything goes in the Pokémon world.
If you're still trying to figure out which Pikachu you want to invest in, make sure you do it soon. The Unova Cap Pikachu will only be available for a few more days—until Oct. 16. Then it'll be time for the next Pikachu to rotate in.