For the next few weeks, you can get Pikachu in a new, distinctive hat each week. Right now, if you enter the code PIKACHU20, he'll be wearing Ash's (Satoshi's) hat from the anime. He also has a new Z-Crystal that does 10,000 Bolt and is pretty badass. If you want a different hat, just wait a week or two to enter the code. According to the Pokemon website, this is the schedule for which hat you get:
9/19/17 – 9/25/17: Original hat (Kanto and Johto regions)

9/26/17 – 10/2/17: Hoenn region hat

10/3/17 – 10/9/17: Sinnoh region hat

10/10/17 – 10/16/17: Unova region hat

10/17/17 – 10/23/17: Kalos region hat

10/24/17 – 10/30/17: Alola region hat


and the Pikachu itself will be:
Level: 1
Nature: Hardy
Gender: Male
Ability: Static
Moves:
Thunderbolt
Quick Attack
Thunder
Agility