How to evolve golbat gen 4

Probably the most obvious way is to put it in your party and walk around with it. The more steps you take with it in your party, the more the Happiness level rises (although walking by itself it a very slow method).

Time spent in the party does NOT add to the Happiness rating.
Win battles with it (especially with the Elite Four), but DON'T let it faint.
Feed it Vitamins (Protein, Carbos, etc.), Rare Candies, and Pokeblocks, but NOT Roots(things that say "It tastes bitter" in the description).
Equip it with the Soothe Bell to make Happiness level progression go faster.
Take it to Contests and win them.
Check the Happiness Rater in Verdanturf every now and then to see if it is ready to evolve.

It may take a while, but it's worth it.

Crobat pwns all the nubs!

As a side note, Nature affects stat growth, not Happiness.

Pokemon ruby crobat

If your Pichu is Impish, it will always be Impish because that is its personality. The Defense stat of Impish Pokemon will grow quicker than usual, while the Special Attack stat will grow slower than usual. Also, your Impish Pichu will prefer Sour Pokeblocks,

how to evolve golbat into crobat in pokemon ruby

how to evolve golbat to crobat pokemon ruby