Along the lines of the smallest possible RC toy

https://hackaday.io/project/162680/log/226525-smallest-possible-rc-toy

autonomous things

https://hackaday.io/project/162680/log/213989-autonomous-thing-which-travels-back-forth

Japan's lunar excursion vehicle

https://global.jaxa.jp/activity/pr/jaxas/no088/03.html

& a sand garden robot

Comes an idea for a portable sand drawing robot based on the lunar excursion vehicle.

It can certainly draw lines.  The problem with this is doing a pen up.  Maybe it needs a quad copter component.  Maybe it can convert into a rolling ball.