kingdom hearts remix question do you have to defeat agrabah before you can go to the next world?

Yes, you have to beat Agrabah before gaining access to Monstro, Halloweentown, Atlantica or Neverland. Granted I think you have to do something in Traverse Town after beating it but after that the doorway should be open. In my opinion, you should do Monstro first...annoying level with a HUGE pay-off (i.e. High Jump). Then (if you do Halloweentown afterward) you can take Atlantica with Pumpkinhead equipped; it'll go so much smoother for you.