You can't 'catch' a crobat. Catch a zubat instead, and train it into a golbat. Golbat evolves at level 22. I decided on a Crobat for my team and it evolved at level 28, I didn't even give it a message, drug, or rare candy. It just got happy from levelling up, if you have a soothebell, give it to your golbat and it speeds things up.