I’ve always thought Two-Face was one of the more interesting Batman characters to dress up as for Halloween. The best part is that you don’t need a complicated outfit to make the idea work. For a Two Face costume, a regular suit can be a good starting point, then you can play around with the two-sided look using different colors and some simple makeup.
I’d also check out a few YouTube videos for makeup ideas before putting everything together. Small details can make a big difference and help the costume feel more like the character without going overboard.