With The Riddler, I decided 16x16px was plenty enough. Could I have given more detail by dropping down to 32px or 64px? Sure. But as you can see, you don’t need to.
I could still do so if I wanted to change the feel of this. Comparing to some of the other characters I’ve done recently, he seems (and is) lower res and less detailed. Next to them, he’s a little out of place.
But by not going into as much detail here, I’m making a point. I’d been doing the last few at a higher level of detail to challenge myself to work at that detail level. But it’s even more challenging, sometimes, to not allow yourself to go to a lower detail level, and force yourself to work at a chunkier resolution. Being able to do either well is challenging, just in different ways. If you always drop down to more detail all the time, try challenging yourself sometime and take that option away, and see how you work with it.