Question

How do you gain happiness in Pokemon white version 2?

Answer 1

Happiness is actually as easy to influence as eating a piece of toast or turning a doorknob, or whatever other comparisons you can think of. The things that will raise happiness include:
-Having the Pokémon in your party
-Giving it Vitamins
-Giving it a massage in Pallet Town, Goldenrod City, Veilstone City, Castelia City or Ribbon Syndicate
-Giving it Certain Berries
-Gaining a Level
-Join Avenue Items

And of course, there are things that will frustrate a Pokémon, causing it to dislike you. These actions include:
-Feeding it bitter food
-Letting it faint continuously in battle

If you capture your Pokémon in a Luxury Ball, the increase in happiness is much larger than if in a normal ball.

There's also one item that influences happiness; the Soothe Bell. As for what it does, it increases the amount of happiness gained.

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Hope I helped. :)

Answer 2

oh there are many ways to gain happiness. the most simple one is battling normally. if you want to gain happiness fast, pick the Pokemon you want to increase happiness, and either bike around for 10, 15 minutes with that Pokemon at the front of the party, or You could also take it too a building in castelia city, where a person will give your Pokemon a massage

Answer 3

Check here.
It includes all methods in all games.

Hope I helped. :)