Usually Gimp dynamics settings are for use with a grapics tablet and pen, as the input device, and generally respond to the user pressure and/or speed of stroke on the stylus. Here are some dynamics settings that can be popped into your user Dynamics folder to add a random element to the drawing of outlines around custom font files using the current brush in my outline filter (link below).

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Here is an example using a star brush (spacing increased) with an outline width of 40 and a RGB gradient of foreground colours black to white. (The colour option, set in the dynamics matrix, uses the current gradient to take its colour data from.)



And one using random opacity.