The Illustrator wrinkle tool / brush is a powerful feature to manipulate and warp and deform paths, how to use ?
It can be found in the width tool section of the toolbar along with the other warping kit.
Select a path in art board (can be used with paths, closed and open, strokes, lines, type and much more). You can double click the icon to display the options to be applied to the selected path.
There are a lot of options to take in such as width + height + angle + intensity + pressure + horizontal + vertical + complexity + detail + brush affects anchor + brush affects + anchor in tangent + brush affects anchor out tangent
There is a lot of randomness with it so if the setting is set to 100% you probably won't get 100% but perhaps something close
Most of the settings have been set to emphasis vertical so you can see no effect on the horizontal (you can see from the image that the horizontal is set to 0 so all the activity is vertically)
If you set the horizontal to 100% and the vertical to 0% it changes the angle by 90 degrees
Anyway, just select the paths and then apply it to the paths (or path) and the distortions will be added but the key thing to remember is that in many cases, a lot of points will be added especially if you set the complexity (great for a scribble like effect combined especially mixed with angle) and also detail. Lots of points can be added to a small region with a very small brush. You can add a lot of points especially to a localized area if you set the settings to low or zero and set a small brush size for the localized area (or the entire set of paths if you have a large brush size) such as setting the width to 1000pt and height to 1000pt especially when the object you are distorting is very small
You can also control the overall intensity of the brush effect via the size as well as intensity, for serious settings set it to 100% (but sadly no more, what is it with Illustrator that the settings rarely can go to 1000%) and if you wish to create only a subtle change with perhaps multiple re-applies then use a low setting of intensity and option vertical and horizontal. Very low intensity requires a number of re-applies to create any noticeable change but it does perhaps give more of a control over the end result, certainly 100% the change can often be quite rapid
Complexity and detail are interesting features, set it low and it is more a warping feature, set it high and a lot more points are added. Double click the icon and set width and height to 1000px and set intensity to 100% and set detail high to add more points or low to have less points and set complexity higher for more points (or lower for less) and set horizontal to 100% and click OK and then apply it to a path.
Much like complexity, keep it low if you don't want to add points and the result is a more fluid warping. Set it high and you will generate a far more complex design
You can use it with open paths as well as closed paths. Just select an open path or create one with the curvature and then apply it to that and you will end up with an intense crinkled line depending on the settings.
If you want to use it just for adding points then set the wrinkle to 0 and set the complexity and detail to a little higher (5 and 2 etc to add a lot of points and complexity). It does need the settings to be all set correctly for it to work so you may find that if you have no horizontal setting and all the lines are vertical then nothing much will happen. You can then use the powerful direct selection or curvature etc to manipulate the points. Select a path and double click the icon and set horizontal to 0% and vertical to 0% and Complexity to 5 and set all anchor to ON and tangents to OFF and OK. Apply it to the segments. You will now see a number of points have been added but no crinkled effect. To move the points, use the direct selection
Another great feature of the setting is that you can modify the anchor and tangent or anchor or tangent and so you can keep the lines or paths in the same place but the shape will radically change but all the anchors will be stuck in the same location. Likewise, the tangent can be set to off and the anchors can be made to move. To affect just the anchor points (and not the tangents) and double click the icon and set the brush affects anchor points to ON and brush affects tangents "in"and "out" to OFF and click OK and apply the effect. The result is a very sharp angled look. In this case, the anchor points are off and the tangents are ON - you can create more rounded designs than the sharper
You can also use the brush setting 'angle' to change the angle of the anchors etc as well as the tangents (depending on the settings) to create lines going off approximately in 60 degrees or 30 degrees etc depending on the setting. Sometimes randomness in the angle kicks in and sometimes not. Again, I would love to see randomness with a little more control to the range of randomness also as well settings to the negative as well as just positive.
It can modify paths (closed or open) in many extreme ways to create some truly unusual shapes even from a basic path such as a circle or square and can also be used to crinkle converted type as well as expanded symbols. It is much like the tweak filter but it comes with many additional features and it can be used like a transform as well. Create a path, double click the icon or press return (if already selected). Set the horizontal to 100% and vertical to 0%. Set angle to 60 and Set anchor points ON only and Set complexity to 10 and click OK. Hold over segments and keep holding for a while. Move to another part of the path
You can use it with paths inside a repeat object (object menu and repeat and radial). The changes with it are reflected in all the paths. You can use this feature to create some truly extreme shapes. In many ways, it works even better with the repeat mirror feature and then combine that with the radial option. It can get quite complex but the results can be pretty magical.
Create a line using the line segment tool, a single 300pt etc and set a stroke of black and width of 2pt. Double click the icon and set the width and height to less than the line length, horizontal 0 and vertical 100% and complexity 1 and angle 0 and intensity 50 and detail 2 and affects tangent handles ON. Apply to a part of the path (sadly you have to close the panel before you can actually apply it). Click over the path and hold and as you do that you will see the line distort only for that part of the brush diameter. If you go back to the same part of the line and re-apply it, it will add even more points and you will get even more distortions up and down with the path. The distortions will never go beyond the initial size of the brush if you apply it in the same position. If you apply it above the original line or below then you will see the distortion increasing further and further away from the original start point and there will be a lot of points in this very complex heart beat line. If you rotate the line by 90 degrees or 45 degrees etc then you will distort the lines away from their original up and down so they become more of a tangle of lines but again, only that area of the applied brush.