In Pokémon Yellow, the player receives a special Pikachu that shows emotions, in a primitive form of the Happiness factor in G/S/C.
There are two events in Pokémon Yellow that are based on its happiness. The first is on Pewter Museum’s top floor—a man whose daughter wants a Pikachu will say different things based on how happy the player’s is.
If happiness ≤ 100:
Your Pikachu looks untamed. May I have it for my daughter?
If happiness > 100:
I’d like to get that Pikachu off you, but it’s too attached to you.
The other instance is in Cerulean City. The character Melanie will reward the player with a Bulbasaur if Pikachu’s happiness is 147 or higher.
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