Purpose:
Acts like a new shape; wormholes!; retro accents.
Parameters and behavior schemes:
Only thing tricky here was the rotation again. I was trying to get the brush to oscillate about the direction you draw, and the sinus function seems like a safe bet. Would get weird results drawing to the left (BI sees this as 0 degrees). If the sinus node isn't offset then the result could be a negative number, and the lowest allowable rotation boundary is 0. Check out the workaround if you like.
Comments on use:
Nothing unusual here.
Hope you like it.
From left to right - spiral, fluid, retro: