shelgon:

A new event has begun. This event gives various hat Pikachu and can be obtained on American, European and Japanese 3DS games including Ultra Sun & Ultra Moon. This runs from today until December 1st. The codes are as follows:

• Hoenn Cap - LETSGOPIKACHU06
  
• Sinnoh Cap - LETSGOPIKACHU09
  
• Unova Cap - 13LETSGOPIKACHU
  
• Kalos Cap - LETS17GOPIKACHU
  
• Alola Cap - LETSGO19PIKACHU
  

Source: Serebii