The secret to this effect isn't a special plugin; it’s the .
Create a new document (1000x1000px, transparent background). Select the (set to "Shape" in the top bar, fill color: black, stroke: none). Draw a shape that looks like a comma or a tadpole: a large circle at the top, which tapers down into a long, sweeping curve. Don't draw the tail straight; give it an S-curve for organic movement.