How to change Deoxys' form to Attack in black 2?
Yes you can. You have to go to nacrene city and go to the museum and in there, there is an exhibit with meteors and you can change its form there. It may not change to attack immediately and if it doesnt, keep talking to it until it does. Source: http://bulbapedia.bulbagarden.net/wiki/Nacrene_City
go to nacrene city museum and click on the meteor