You can either:
Have Poketch App #6, which tells you your pokemon's happiness when you press and hold it by the number of hearts that appear above it. If it has two large hearts, it means it loves you the most, whereas no hearts mean its happiness is 0.
You can also go to Dr. Footstep's house on route 213. If your pokemon's happiness is at max, he will give it a ribbon.
level up your GOLBAT with high happiness.
It evolves through happiness
It evovles with max happiness
Level it up when it its happiness is full
Any level, just get it to max happiness.
It shows how much the Pokemon is happy with you. In some Pokemon you can evolve it if it has high happiness.
you cant find it. get an eevee, max its happiness, level it up at night, and tada! you have an umbreon!
level 30
It evolves by Level Up + Happiness at 220. You can't tell what your Pokemon happiness is though.
It has to have happiness. :)
You have to evolve it with its happiness level at 220.
Happiness maxed
level up your GOLBAT with high happiness.
Level it up during daytime after increasing its happiness level. I believe there's a lady you can talk to in Northeast Goldenrod City that tells you the happiness level of the first Pokemon in your party. You can easily increase a Pokemon's happiness level by using items on it, especially vitamins (Carbos, Protein, etc.) It just takes a little time.
You have to have it have high happiness. It doesn't evolve at a level.
Golbat evolves into Crobat when you level it up with high happiness.
Happiness is gained by taking care of your pokemon giving it items, training it and many more things. Once it's happiness reaches the max happiness have it level up to evolve the pokemon.