I’d never tried molding fondant before I made this cake. I followed the tips in this tutorial and found them wholly insufficient. Maybe it’s because I was using silicone ice cube trays as opposed to molds made specifically for fondant/gumpaste, but I found that simply kneading extra sugar into the fondant was not enough - I needed to generously dust the mold with powdered sugar, and straight-up roll the fondant in a pile of sugar before pressing it in. Freezing it in the mold DOES help quite a lot, although the pieces do get VERY sticky from condensation for a while between unmolding and drying out.
By far the hardest part was sculpting the hair/hats/headpieces. Those f***ers are tiny.
You probably mean Dark Knight Batman. I’ve never been asked to make something dark (theme-wise) like that; my style is quite a bit more…whimsical. I look forward to trying sometime, though. The main obstacle that springs to mind is that black fondant is both gross and terrible to work with; by the time you get enough food coloring into it to make it black, it tastes terrible and the texture is shot. If I were to make a Dark Knight cake, I’d have to order some black Satin Ice or something.
But! I have, in fact, made a Batman cake before. Two, as a matter of fact. One of them was just this past weekend; it’s coming up next in the queue. The other one was for my little guy’s 2nd birthday. Both of my boys were really into the Adam West Batman movie at the time, and blue and yellow are far, far easier to work with than black and gray.

This was a frozen buttercream transfer; I’ve talked about how to do them before. This was the first time I used a transfer for the entire top of the cake; as you can see, it came out rather lumpy. I pay a lot more attention to making sure that the back of the transfer is smooth, now.