Here’s a sketch using a brush Im working on. I’m enjoying this one a lot, but I’m just trying to get the medium texture right before I release it to the shop. The brush behaves like an oil paint or pastel, but the low end range acts more like a watercolour. Although it’s all digital and real world rules can be ignored, if a brush has relatively close equivalents in real natural media it’s a bit jarring when it veers off into other media too quickly.
It can be a bit too dissonant, like awkward notes or unusual timing in music. When it’s off enough though, and the look you are going for bears little to no resemblance to anything in the real world there is a lot of room for digital brushes to be as quirky as you want them to be.