I just used this tutorial to make a tutu--so simple and it turned out so well. Don't forget to look at her updated instructions for cutting the tulle.
How to Make a Tutu - I think this would work better than the other methods I have tried.
Batman or Robin costume fluffy tutu by Victoriacouturepink on Etsy
Twylie wanted to be Batman this year do Halloween but I already had a costume so maybe this next year.