I want to get a brush working like in Adobe Illustrator Draw where the ends are thinner than the main body. I cannot figure out how to apply a fake pressure like this without having a drawing pad/tablet, but I know this exists. I'm using the latest Illustrator CC. Thanks!
Okay so first I have to tell you that there is no way you can simulate pressure with a mouse. It just cannot work since you will need to provide a value of pressure before you draw the line and then provide another value of pressure for the end of your line.
As you can see it would be very difficult but don't worry there is hope. You can make an outline of what ever artwork you wish to make with your mouse using the brush tool. Then you can edit the brush strokes with the direct selection tool and add depth and variation in the brush strokes by altering the position of the anchor points. I know it sound like a lot of work but adding a little depth and make basic artwork look impressive.
I hope my answer helps.
There is the width tool (SHIFT + W), you should be able to achieve your desired effect with it.
First you draw a line with the pen tool, then use the width tool to change the width along the line.