
The brush system in Moho is not really able to create this kind of line, but I found a workaround
Here's an example. From left to right: no strokes, strokes with no brush & strokes with this new uneven brush

The trick is I created an 'animated brush' (it's just a circle changing its size) and exported that animation as an image sequence

And then put that sequence in a folder inside of the Moho's Brushes folder (in the Custom Content folder)
If select the new brush and uncheck 'Random order', Moho will follow the sequence order to paint the brushes, smoothly making the brush smaller and bigger across the line.
In a way, it is as if the vector line were the timeline
Here you can download the brush with some settings that work well for me:
https://www.dropbox.com/s/ckav9thpcmz99 ... .zip?raw=1
And here's another WIP example I'm preparing:

Please let me know what you think and if you have any other ideas that could work with this 'animated brushes'.