Happiness is a number between 0 and 255 that gauges how friendly a Pokémon is towards its trainer.
Every Pokémon starts with 0 happiness, which will change based on certain events:
- Keeping the Pokémon outside of its Poké Ball will cause it to slowly gain happiness.
- Leveling up the Pokémon will raise happiness.
- Letting the Pokémon faint will lower happiness.
- Using a Pomeg Berry, Kelpsy Berry, Qualot Berry, Hondew Berry, Grepa Berry, or Tamato Berry on a Pokémon will raise happiness.
- Using an HP Up, Protein, Iron, Calcium, Zinc, or Carbos on a Pokémon will raise happiness.
- Trading the Pokémon will reset its happiness to 0.
- Capturing a Pokémon in a Friend Ball will set its initial happiness to 200 rather than 0.
- Capturing the Pokémon in a Luxury Ball or letting the Pokémon hold a Soothe Bell will cause events that raise happiness to increase happiness by an additional one point each. These two conditions can stack with each other.
Evolution
A happiness of 220 or more upon leveling up is necessary to evolve: